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chevynut
11-08-2015, 09:23 PM
While at SEMA this past week I talked to several companies about parts for my 502. I bought the engine (a NEW GMPP ZZ 502 longblock) from a guy over 12 years ago for a great price and it's been sitting around in and out of my car ever since. The exhaust ports have been covered with duct tape and the intake loosely attached. I sold the intake that came on it along with the HEI distributor. I bought all the parts to make it a GMPP Ramjet 502 with some upgrades. I added new GMPP upper and lower intake manifolds, all new sensors, IAC valve, GMPP computer-controlled distributor, 42 lb/hr injectors with a GM fuel rail and regulator, a Holley dual 58mm 1000 CFM throtlle body, MSD coil, and a Holley Commander 950 PRO with a Wideband O2 kit. This is the way it looked when I bought it and it's never been run...

http://www.trifivechevys.com/attachment.php?attachmentid=5216&stc=1

The engine has been sitting for a long time, in a dusty environment, and has some issues I want to address so I have decided to tear it down completely, clean it up, and freshen everything to get it ready for final assembly of my car. I also want to paint it. I don't intend to replace a lot of parts, just clean everything up and make sure it's put together right. I'll replace a few parts with better ones but try not to go overboard ;).

Rings-

I know these engines have low tension oil rings and that's one thing I definitely want to address. I don't want this to burn oil like some I've read about. I talked to a rep at the Total Seal booth about his recommendations and come to find out he worked 20 years at GM and worked on the development team for the 502. He said I am on the right track to change the rings, and agreed that I should go to regular tension oil rings. He suggested I buy a complete set of file-fit rings, lightly hone the cylinders with a torque plate attached, and re-assemble the engine. I asked about pistons and he said leave them alone, because the engine is very well built otherwise.

I looked in their catalog and they sell a set of conventional rings, or a set that contains a gapless top or second ring. I like the concept of at least one gapless ring so I think I'll probably go with a set that has a gapless top ring (seems to make the most sense there), a conventional second ring, and a set or normal tension oil rings. Does anyone here have experience with the Total Seal gapless rings?

Cam-

I have been considering upgrading the cam for a while now. At SEMA I talked to Comp Cams about the camshaft and other engine parts. Again, the guy said the engine has some very good parts in it and he recommended that I have the engine balanced since he said GM doesn't do a very good job of balancing them. I really wonder how important that is for my purposes.

He also recommended a slight cam upgrade for me because he said the most often heard complaint about the ZZ502 is the mild cam and lack of lopey idle which most guys like. The stock ZZ502 cam has 224/234 duration @.050", a 110 degree lobe separation angle, and .527/.544 lift with 1.7 rockers.

The cam he recommended is their XR282HR-14 hydraulic roller that has 230/236 duration, a 114 degree lobe separation angle, and .510/.520 lift with 1.7 rockers. The only thing that bothers me about this cam is the lower lift. It seems like with the longer duration I'll get more of a lope, but the performance gain isn't obvious to me at all. In fact it seems like I should lose bottom end torque with the higher lobe separation angle.

The next cam is their XR288HR-14 which has 236/242 duration @.050", a 114 degree lobe separation, and .520/.539 lift.

The stock ZZ502 cam has more lift than either of these Comp Cam rollers, but not as much duration. Which is the better choice for a strong street cam? Will either one make more power than the stock one, and how much? I always thought a short duration high lift cam was better for street use.

In this article they "wake up" a ZZ502 with a larger Comp cam that has 242/248 duration, 112 lobe separation and .566/.566 lift. They gained 80 HP and 27 ft-lb and lowered the peak torque 300 RPM. The weird thing is their catalog I picked up says this cam is for jet boats. :)

http://www.superchevy.com/how-to/engines-drivetrain/1504-get-more-power-from-a-chevrolet-performance-zz502-crate-engine/

Rockers-

I asked Comp Cams if there were any roller rockers that would fit under the factory 502 valve covers that I intend to use..cuz I like them ;). He suggested to use their roller tip rocker, the Comp Cams Magnum rockers with 1.72 ratio. This seems like a reasonable upgrade even though it's not a full roller rocker which won't fit under the stock valve covers. I wonder why the 1.72 ratio instead of the stock 1.7?

Head gaskets-

I assume I'll have to replace the head gaskets so next I ran into the Cometic booth and talked to them about their gaskets. I asked why their head gaskets are better than others, and got the whole marketing rundown. I have since done some research and read that some guys have water sealing problems with these multi-layer steel gaskets. Plus their head gaskets are about twice the price of others.

So, are head gaskets re-usable if the engine hasn't been run? I think once they've been torqued, they're shot but thought I'd ask anyhow ;). My block has a 4.466" bore and I've seen head gaskets of sizes all around that number. What size gasket bore do I need to get? Also, what about thickness? I see them from .027" to .070" thick.

After doing some research it seems like a composite head gasket is less likely to cause headaches. I'm not building a race engine either, but I don't want problem with head gaskets. Lots of guys seem to like the Fel-Pro composite gaskets. Now I need to know which one to use. I could just stick with the GMPP 12363411 gasket they originally used on the engine which has 4.540" bore and is .039" thick. I don't know who makes them.

Seals-

My engine has a one-piece rear main seal...do I need to replace it? I have no idea if they degrade with time, even if unused. I have a new oil pan gasket and I believe I have new intake gaskets as well. What about valve seals?

Any other upgrades you would recommend while I'm in there? I don't plan to do any porting of the heads or any other machine work. My plan is to disassemble the engine, remove the oil galley plugs, make sure everything is clean as I can get it, and re-assemble it using the new parts listed above.

MP&C
11-09-2015, 04:46 AM
So here's where everyone can make suggestions on how Laszlo should spend his money.... This can't end well... :p

markm
11-09-2015, 06:09 AM
The story goes that OEM steel are not exactly 1.7 some may be 1.65. Rollers are designed to give you at least advertised numbers.

Cam selection depends on use of car. I really do not see you in drag races or cross country runs.
I run a 425hp 427 cam in my 396 244/244@ .050 and .520 lift. It works well for what I do, I like a cam with some duration. My favorite cam is the 30/30 Duntov in my 67 Camaro. I also like solid or roller lifters not a fan of hyd. or hyd. roller. What is the current cam.

The only reason I can think of for using a thinner head gasket is if you are trying to squeeze a little more compression out of it.

NickP
11-09-2015, 06:41 AM
At this stage of my life, I no longer see the need to have a near perfect, near race engine in a vehicle unless the specific build requires it for a specific application. The expense outweighs the disadvantages. I am more drawn to reliability than the lumpy cams and fuel mileage than horse power. I know this is a very subjective topic and I know what is involved by going to the extreme with power plants. If it's bragging rights or one just wants it because one can, I fully understand that.

I feel that anything over 350 HP is a waste. There are very few places in the USA one can bust it off and do anything above 75 MPH legally.

Just Kidding!!!!!!!!!!!!! For me, fresh means new. New head gaskets, new rings, new seals. I'd save my money and use the same cam, lifters etc.

Troy
11-09-2015, 06:58 AM
Won't all of this work void your warranty? :D

chevynut
11-09-2015, 07:44 AM
Nick, that's essentially what I'm trying to do. Spend money where it makes sense, but not go to extremes anywhere I don't need to. This engine has a lot of good parts in it already and it should make 500-550 HP as-is.

Troy, I think the warranty expired when I bought it. LOL! :) I thought it was going to be running in two or 3 years.

What do you guys think about the balancing? I'm feeling like it's a waste of money to do that for the type of use this engine will see. If it's good enough for GM to ship that way it seems like it should be good enough for a street engine. I'm not sure I'll see any gain in reliability or anything.

I did some more looking last night and I think I'm staying with the GMPP head gaskets that were made for this engine.

I also noticed the gapless ring set is over twice the price of a standard set of rings from Total Seal. Would that be worth the money? I don't mind spending some money on the engine but I don't want to throw it around needlessly. The honing with the torque plate seems to make sense but it will be a hassle. I just don't want an oil-burner.

Would you do anything to the valves, valve stem seals, or springs? The valve springs have been sitting compressed all this time in some cylinders. I'm not equipped to do any of that myself.

I've considered having a local shop build up my longblock for me but it would be fun to do it myself too.

JT56
11-09-2015, 08:53 AM
I have run cometic before...they fit extremely well. Never had any issues with water sealing, but that was before boost. I went back to Felpro MLS and have no issues.

Rick_L
11-09-2015, 11:55 AM
Given the oil consumption reptutation of those engines, changing to a "more standard" oil ring makes sense. I personally feel there's no benefit to the gapless second ring - all it does is fool you on the ring condition when you do a leak down test. On the other hand, I just helped tear down a street driven 468 BBC that had them and everything looked really nice. So I don't see a down side to them except for the above comment + slightly more cost. Honing with a torque plate is probably a good thing. File to fit rings aren't something needed for your type of engine, but again no downside. Just slightly more trouble + cost.

On the cam, I think the cam in it would be fine for what I think you'd use the engine for, but the 230 @.050 Comp will probably pick up some power.

I understand why some like cams that idle badly, sounds good in the parking lot, but it's not helping you out except for the "sound" and there's a price to pay.

I don't think that the tiny bit of difference in lift means anything relative to your use of the car and its performance. The performance is in the area under the lift curve, and you gain that with either duration or lift or both. Really good all around engines flow a lot of air at low lift, don't need high lift so much.

The gain with that Comp cam is more about the duration than the lift.

Keep in mind that getting the idle tune and driveability right with the Holley controller will be more difficult with a bigger cam. It probably will like more timing at idle and off idle than the stock cam, but with EFI fixing that doesn't screw with the rest of the timing since it's tables and not analog with springs and weights. There
s probably a Holley tune for a BBC that will get you pretty close for startup.

markm is correct on the stock rockers, they are "not quite" a true 1.7 ratio, the roller tip ones will be.

If I were you, I'd buy a new Fel Pro or equivalent gasket set. It should have a new rear main seal, I'd put it in since it will be on hand. Probably don't need to, but you might as well. There's nothing wrong with Cometics, but Fel Pro is more widely available (you can get it locally), and frankly there's no wrong answer on head gaskets as long as you stay with the typical composition gasket that's widely used and what your engine came with.

Valve springs sitting compressed in storage aren't affected at all. On the other hand the factory didn't shim them at all, there will be no precision or consistency. IF you go with the Comp cam, look at the recommended valve springs for it, they are likely a bit more than the stock spring, and it would be worth a little high rpm performance to get them and shim them to get the actual recommend seat pressure.

Given that you live in the high desert, if the engine has been stored dry and clean, I'm not sure I'd do anything. It's just time and money that might have better return elsewhere. Especially as in it might be done sooner.

chevynut
11-09-2015, 12:22 PM
Given the oil consumption reptutation of those engines, changing to a "more standard" oil ring makes sense. I personally feel there's no benefit to the gapless second ring - all it does is fool you on the ring condition when you do a leak down test. On the other hand, I just helped tear down a street driven 468 BBC that had them and everything looked really nice. So I don't see a down side to them except for the above comment + slightly more cost. Honing with a torque plate is probably a good thing. File to fit rings aren't something needed for your type of engine, but again no downside. Just slightly more trouble + cost.

Thanks for the feedback Rick. Total Seal says you can use the gapless ring in either the top or the second groove. I figured the top made more sense, but maybe it doesn't. I thought ALL rings were file to fit rings. If that's not the case, are they that accurate coming out of the box? When I rebuilt my Yamaha Grizzly top end last year I had to file fit the rings. I have a standard bore and don't expect that to change unless I run into some surprises when I tear the engine down...hope not. :eek:


On the cam, I think the cam in it would be fine for what I think you'd use the engine for, but the 230 @.050 Comp will probably pick up some power.

I understand why some like cams that idle badly, sounds good in the parking lot, but it's not helping you out except for the "sound" and there's a price to pay.

I don't think that the tiny bit of difference in lift means anything relative to your use of the car and its performance. The performance is in the area under the lift curve, and you gain that with either duration or lift or both. Really good all around engines flow a lot of air at low lift, don't need high lift so much.

The gain with that Comp cam is more about the duration than the lift.

Keep in mind that getting the idle tune and driveability right with the Holley controller will be more difficult with a bigger cam. It probably will like more timing at idle and off idle than the stock cam, but with EFI fixing that doesn't screw with the rest of the timing since it's tables and not analog with springs and weights. Theres probably a Holley tune for a BBC that will get you pretty close for startup.

Yes Doug Flynn sent me a tune for a BBC with close to my setup to get started. I'm not sure a cam change is worth it unless I gain some significant HP and don't sacrifice any low end. That's what was interesting about that jet boat cam.


markm is correct on the stock rockers, they are "not quite" a true 1.7 ratio, the roller tip ones will be.

I agree. But the roller tip ones are advertised as 1.72 ratio. I don't think that will change anything but I like the idea of reducing friction there.


If I were you, I'd buy a new Fel Pro or equivalent gasket set. It should have a new rear main seal, I'd put it in since it will be on hand. Probably don't need to, but you might as well. There's nothing wrong with Cometics, but Fel Pro is more widely available (you can get it locally), and frankly there's no wrong answer on head gaskets as long as you stay with the typical composition gasket that's widely used and what your engine came with.

A gasket set may be the way to go but I'm not sure if that's the case with this engine and I don't see where GMPP offers any complete sets. The GMPP head gaskets for this engine are $79 each from Summit. The only other gaskets I really would need are the timing chain cover, since I have everything else. The oilpan gasket and valve cover gaskets are rubber and are reusable. I think I even have a brand new pan gasket.


Valve springs sitting compressed in storage aren't affected at all. On the other hand the factory didn't shim them at all, there will be no precision or consistency. IF you go with the Comp cam, look at the recommended valve springs for it, they are likely a bit more than the stock spring, and it would be worth a little high rpm performance to get them and shim them to get the actual recommend seat pressure.


This engine redlines at 5800 RPM and I doubt I'll try to push it over that limit. Again, thanks for the advice on that since an engine builder would probably try to talk me into some different springs. The Comp Cams rep said not to mess with them.


Given that you live in the high desert, if the engine has been stored dry and clean, I'm not sure I'd do anything. It's just time and money that might have better return elsewhere. Especially as in it might be done sooner.

That's the issue...it's been dry but not very clean. I think the injector openings have been unplugged this whole time and the intake was only on with a couple of bolts. My shop is really dirty when we work in there so I'm concerned some grit may have found it's way into the engine. I'd rather be safe than sorry, and I feel that I NEED to address the low tension ring issue so it has to come apart.

Thanks a lot. ;)

markm
11-10-2015, 05:59 AM
"Would you do anything to the valves, valve stem seals, or springs? The valve springs have been sitting compressed all this time in some cylinders. I'm not equipped to do any of that myself. "

Really, KD sells several affordable valve spring compressor options, this is easy compared to some of the stuff you do on suspension. I do have to agree with you about doing it yourself. That is why I will never have a crate moter.

chevynut
11-10-2015, 07:50 AM
I understand what you're saying Mark, but the question is whether I need to do anything to the heads. If the springs are fine I'll probably just leave them alone. Seems like the seals should be okay too.

A crate engine is a great deal if you can find what you want and can install it and run it in the warranty period. I was recently told that GM has done something in the ECUs that monitor when the engine is actually run, and starts the warranty at that point instead of when you bought it. Good idea, since a lot of us take a lot longer to build our cars than we think.

I got this engine for $4400 and sold the intake and HEI distributor for a couple of hundred bucks. The partial engine costs $7500 today. I have about $6500 in it with the Ramjet intake, sensors, TB, injectors and ECU and a new Ramjet 502 is over $11K, so I guess I can spend some money on it and not feel bad. :)

hutchenc
11-12-2015, 06:27 PM
Laz...I had a custom cam ground for my 421 SBC by Mike Jones. I told him I wanted a cam that was tame on the street, didn't need crazy valvesprings, peaked around 6200 to 6400 RPM, and is optimized for high altitude. The specs on it are 240/238 at .050, 108 LSA, and .600/.557 lift with 1.6:1 roller rockers. The reverse duration split is intended to slow down the exhaust valve a bit because of the altitude...Ft. Collins isn't as high as Laramie, but you're not exactly at sea level either. I've driven it plenty and it drives pretty well for a relatively big roller cam. Until you hit the loud pedal, you can't really tell it's there...there's some lope, but nothing crazy. It's not real happy driving in high gear (which for me is 4th) below 1300 RPM though. If that cam in a motor that's a solid 80 cubes smaller than your 502 can tolerate that much duration yours certainly can. It was not much more than an off-the-shelf cam...$100 more to be precise.

Not sure what the power curve on the 502 is like, but I bet it's outta wind at 5,000 RPM with a cam that small.

Also...roller tipped rockers...wouldn't bother. If you're going to upgrade, get full rollers. Take a look at the upgrade GM made with the LS valvetrain and that should tell you what they think about roller trunions vs. roller tips. ;)

Probably not worth it to do much to the heads themselves unless you decide to start drag racing your Nomad.

Rick_L
11-12-2015, 07:14 PM
I assume that your unusual extra intake duration compared to the exhaust is a "crutch" for the elevation - makes sense to me. The 108 degree LSA is another thing that helps that. Years ago with race engines that had limited heads we ran 104 LSA, it kills low end but helps with peak power. The 240/238 with 108 LSA makes some sense. You could keep the same relative numbers and vary the duration up or down to suit the desired torque curve. Remember though, this is fine tuning, this is not going to be a huge change.

There's no doubt that a full roller rocker would be better, actually a fixed shaft system would be better yet - but I think that the stamped steel with roller tip recommendation is based on it fitting under the short 502 rocker arm covers. I think it's adequate for what I think Cnut wants to do with the engine.

chevynut
11-12-2015, 07:35 PM
The specs on it are 240/238 at .050, 108 LSA, and .600/.557 lift with 1.6:1 roller rockers. The reverse duration split is intended to slow down the exhaust valve a bit because of the altitude...Ft. Collins isn't as high as Laramie, but you're not exactly at sea level either. I've driven it plenty and it drives pretty well for a relatively big roller cam. Until you hit the loud pedal, you can't really tell it's there...there's some lope, but nothing crazy.

I haven't really studied up on cam specs and valve timing much, but back in the "old days" we talked about "overlap" which is the time the intake and exhaust valves are both open. This is what I always understood causes the lope at idle. I thought by increasing the lobe separation angle you essentially increase overlap with the same duration? So that's why I though the XR282 cam had more lope, because of the 114 degree lobe separation angle versus the stock 110 degrees.

I would think a SBC and a BBC would sound about the same as far as idle lope if the cam durations and lobe centerlines were the same. It would stand to reason that your cam with 109 degrees lobe centerlines would idle well, I think.


The beauty of a roller cam is that you can use higher lift rates than you can with flat tappet cams, and therefore increase the "area under the curve" and get more air/fuel into the cylinder at the same lift and duration. They also decrease friction.
It's not real happy driving in high gear (which for me is 4th) below 1300 RPM though. If that cam in a motor that's a solid 80 cubes smaller than your 502 can tolerate that much duration yours certainly can. It was not much more than an off-the-shelf cam...$100 more to be precise.

Not sure what the power curve on the 502 is like, but I bet it's outta wind at 5,000 RPM with a cam that small.

The Ramjet 502 has over 500 ft/lb of torque from 2000 RPM up. It peaks at 4200 RPM at 567 ft-lb. I believe it's "out of wind" due to the small throttle body on it, which is the same 635 CFM unit used on 350s. That's the reason I went to a 1000 Holley TB. I believe the torque curve will stay higher longer with this bigger TB, and guys I have talked to that have changed theirs say the power curve was greatly improved. I also went to a 42 lb/hr injector because I had no injectors and calculations suggested the 42s were a better choice than the stock 36s.

So once the TB is out of the equation as a restriction, the next thing is the cam. I think the heads on this engine are great, and they have 2.25" intakes and 1.88" exhaust valves with big oval ports. I don't remember what they flow.

I don't want a cam that shifts the power curve to the top end and sacrifices bottom end torque. If you read the article I posted about, they used a marine cam and shifted the torque curve DOWN 300 RPM and gained 80 HP and 27 ft-lb. That's the kind of thing I'd prefer to see, rather than putting all the power at the top end. Street driving is a lot "seat of the pants" and I want torque "now". ;) So why do they advertise this as a marine cam?

Thanks for the help. It's been years since I've dealt with this stuff and I'm re-learning a lot of things....and a lot that has changed.

hutchenc
11-12-2015, 08:46 PM
I think you have it backwards Lazlo. A wider LSA will decrease the amount of overlap vs a tight LSA...think of two cam lobes moving away from each other around the camshaft's long axis therefore reducing overlap. There's a lot of info about the pro's and con's to wider vs. narrower LSA, but from what I understand, a wider LSA makes a car idle better and is more friendly with EFI. Look at the LSA's for the newer GM motors...115+. I think a wider LSA also lets a motor "hang on" to higher RPM power for a little longer vs. a narrow LSA which will fall off faster after peak. Additionally, I think the wider LSA makes for a flatter power curve vs. a peakier one with a narrow LSA. Rick can correct me if I'm wrong.

And Rick...yep, you're right. The split duration is a crutch for the lack of oxygen at high altitude. And with really good heads, I didn't need the same lift on the exhaust either. Would be interesting to experiment with different ratios, but it's plenty fast and I'm not chasing tenths with it!

And yeah...the roller tips are probably not a bad deal if you want to retain stock valve covers and might regain the original 1.7:1 ratio over a set of stamped rockers. I almost wen with 1.7:1 shaft rockers on my SBC (which has AFR 220 heads...they needed offset shafts to get the right valvetrain geometry, but didn't need shaft rockers)...the cost was prohibitive as it would've added close to another $1,000 to the total, and I spent way too much as it was to begin with on that little beast!

Laz...you might call a few cam grinders and see what they recommend. Mike Jones was easy to work with. I've heard good things about Ed Curtis and Bullet cams as well. You could also call Mike Lewis of Lewis Racing Engines (http://www.lewisracingengines.com/)...Mike is based out of CA, he built my 421 and worked directly with Mike Jones on the cam. Mike Lewis is good people, big time! He knows what he's doing (and doesn't just build race engines...I also think he has soft spot for big blocks) and might be able to help you with some of your other questions about rings, head gaskets, etc. Also, his prices were right in line with Summit/Jegs for parts so that's also something to think about.

Rick_L
11-13-2015, 05:20 AM
Hutch nailed it with his summary of narrow vs. wide LSA. Narrow LSA = more overlap and a peakier torque curve with (maybe) more peak power, and wide LSA = less overlap and a broader torque curve with more average power. There are some other variables with LSA selection like intake flow and compression ratio, but that's beginning to split hairs.

Relating this back to my race engine example, when we were running an SBC with limited cylinder heads about 13:1 compression, we ran 104* LSA. My last race engine with some really good heads and 17:1 compression, we ran as much as 114* LSA. And that engine idled much better than many would expect even with 276* intake duration @.050".

Troy
11-13-2015, 07:47 AM
Just throw a 3/4 race cam in it and it'll go like a raped ape!!!:D

chevynut
11-13-2015, 08:18 AM
I think you have it backwards Lazlo. A wider LSA will decrease the amount of overlap vs a tight LSA...think of two cam lobes moving away from each other around the camshaft's long axis therefore reducing overlap.

I was wondering about that after I wrote the above post. I just assumed that since the COMP cam rep suggested the cam with the 114 LSA to increase the idle lope that was what increased the overlap. After looking at this diagram from Lunati what you say makes sense:

http://www.lunatipower.com/Tech/Cams/CamSpecTerms.aspx

So what I don't understand now is how going from the stock 224/234 110 LSA to the 230/236 114 LSA for the XR282 cam increases lope as COMP suggested. I understood a lopey idle was caused only by increasing overlap. I think I can calculate overlap by adding the intake and exhaust duration and dividing by 4 (since it's in crank degrees) and subtracting the LSA, assuming symmetrical lobes. If I do that I get 4.5 cam degrees (9 at the crank) overlap for the stock 502 cam and 2.5 cam degrees (5 crank degrees) for the XR282. That's a decrease in overlap.


from what I understand, a wider LSA makes a car idle better and is more friendly with EFI. Look at the LSA's for the newer GM motors...115+. I think a wider LSA also lets a motor "hang on" to higher RPM power for a little longer vs. a narrow LSA which will fall off faster after peak. Additionally, I think the wider LSA makes for a flatter power curve vs. a peakier one with a narrow LSA. Rick can correct me if I'm wrong.

I'm not sure how EFI affects choice of cams, but how does a cam with 242/248 duration and 112 LSA result in lowering the peak torque RPM as in the marine cam article? The overlap increases dramatically to 21 crank degrees so the idle lope is probably pretty wild. It has a wider LSA than the stock 502 cam. I wonder if it's the timing (cam centerline)? I would think someone has built a model for all of this stuff. :)



And yeah...the roller tips are probably not a bad deal if you want to retain stock valve covers and might regain the original 1.7:1 ratio over a set of stamped rockers.

Yeah that's the objective. I like the looks of the stock valve covers myself, better than sheetmetal ones or most of the cast ones I've seen. The roller tips are a good idea imo and the rockers don't cost that much and are probably better than the stock ones and will reduce friction a little. Most of the friction is probably at the ball to rocker, though. The article on the marine cam said their roller rockers interfered, but not by much. I would use full rollers if I could get them under the valve covers....I think it's the adjuster nut that interferes. Does anyone make some type of valve cover spacer? Or is there some other set of full rollers with a shorter nut? Why can't the standard locking nut be used with them?



Laz...you might call a few cam grinders and see what they recommend.

I might do that. The cam variables aren't that many (duration, lift, LSA, timing/centerlines) but there's a lot of combinations to consider. I don't see any timing specs in the COMP catalog....but it would just add to my confusion anyhow :confused:.

chevynut
11-13-2015, 08:21 AM
Oh yeah, after reading Rick's post I recalled reading an article about static versus dynamic compression ratio. As I understood it different cams resulted in different dynamic compression ratios but I don't remember the specifics. Is that how you got away with running 17:1 compression??? :eek: Never heard of anything that high with a gas engine. My 502 only has 9.6:1 compression, but I understand that is not a big deal with the right cam.

chevynut
11-13-2015, 09:19 AM
I just found this article that I thought was very informative. Looks like a thinner head gasket might help me a bit and actually decrease the chance of detonation.

http://www.hotrod.com/events/coverage/0311em-power-squeeze/

Combustion Chamber Dynamics
A cool charge may be the first step toward utilizing a higher CR, but what happens in the combustion chamber can make or break any such efforts. A prime factor here is never to loose sight of the fact that the faster the charge can be burned the higher the compression the cylinder will stand. Chamber cavities between the piston and the cylinder head between about .060-inch - .0120-inch appear most likely to be the site of detonation. Speeding up combustion mixture motion/agitation is vital. This means maximizing the quench action. On a small-block Chevy with a stock block height, a stock compression height piston is typically .025-inch down the bore. With a .040-inch gasket this makes the static quench clearance .065-inch, which is way too wide. By cutting the quench clearance the burn rate and quality improve to the point where the motor gains compression and is less likely to detonate even at the higher ratio involved.

So how closely can the pistons approach the head face? Although it comes under the heading of "don't do this at home" I have run the static piston/head clearance down to as little as .024-inch in a 350 with stock rods and close-fitting hypereutectic pistons. The pistons just kissed the head at about 7,000 rpm. As far as power is concerned, an associate of mine ran some tests in a nominally 450-horse 350 and found that each 10 thousandths of quench reduction was worth approximately 7hp. If you are building from scratch, make maximizing the quench your number one priority toward achieving compression and avoiding detonation.

There's also some good stuff on DCR. ;)

Rick_L
11-13-2015, 10:09 AM
My 17:1 engine ran fuel that was designed for that. On a race engine you want the DCR to be as high as practically possible, once you've established valve timing. High duration cam timing reduces DCR.

DCR discussions apply to street engines and fuel characteristics. Race gas is not legal for the street, and even if it was, you have availability and cost problems.

You can calculate the theoretical effect of increasing compression ratio with the math that's presented in any IC engines textbook. The effect trends to asymptotic (further increases have smaller returns), but the slope is always positive.

Part of the lope deal has to do with the opening ramps vs. the duration @.050" lift. A good example is the Duntov 30-30 factory cam for the SBC. It has a fairly moderate duration @.050" but it is a huge cam if you measure duration at .005" lift. This gives you a lot of overlap at idle which makes it lope and idle badly. It also bleeds off a lot of DCR, which means you need a lot of compression with it. Factory engines that used that cam had advertised 11:1 CR. It's also why an aftermarket cam with less duration @.050, particularly a roller, will make more power than a Duntov 30-30. Comp Cams "Thumper" cams are another example. They are ground to intentionally produce a lope.

So if you're looking for bad idling and lope, you probably should be comparing overlap at full advertised duration.

Keep in mind that camshafts that produce lope will require a lot more tuning work at idle and low speed/low load with EFI to get them to idle at all and have driveability. They usually respond to more ignition timing in these areas, but without increasing timing at higher rpms/more throttle opening. Actually this is true of a carb engine also.

chevynut
11-13-2015, 11:01 AM
I'm not really looking for "bad idling" or more lope. I had a guy at Goodguys fire up his 55 Chevy with a 502 in it and I thought it sounded great. Just enough lopey idle that you could tell it had something in it. I guess what I'm looking for (if anything) is a cam that will give me the most torque throughout the RPM range. I don't want to sacrifice low-end torque and move it all to the high end, nor do I want to go the opposite direction because I'll lose peak HP. I want to take full advantage of the big heads and the larger throttle body I added to the engine while keeping the streetability. It sounds like I might want to look at increasing LSA and maybe that's what the Comp XR282 gives me. I still don't understand why it would give more of a lopey idle with the lower overlap...any comment on that?

My goal is to try to "fix" the big drop in torque after 4200 RPM. I "THINK" that's due to the dual 48mm 635 CFM throttle body, but if the cam is also a limiter I'd like to address it. The peak torque is 567 ft-lb. If I can extend that further up into the RPM range while not losing it down lower I could increase HP a bit. I'd like to get into the 550-600 HP range without a lot of hassle if I can. Of course, I don't expect that at 5100 feet elevation.


http://www.pswired.com/misc/pacaudio/saturnstyl/dyno10001.jpg

Rick_L
11-13-2015, 03:18 PM
Again, compare the overlap at "advertised duration" vs. the overlap at .050" lift duration.

Keep in mind that the rep at the booth may not be the sharpest pencil in the drawer or really know anything about the cam you already have. Call Comp's tech line and ask the same questions and see what the next guy tells you.

Also keep in mind that there's not going to be a huge difference in the performance of those 2 cams, you are getting very close to hair splitting territory.

You are going to lose about 20% of the sea level power at 5000'. You will still have enough torque to spin the tires with either.

hutchenc
11-14-2015, 02:41 PM
Really think you should call an experienced cam grinder and see what they say. Comp's tech line probably won't have the most knowledgeable guy on the other end of the phone.

Check out this thread Laz: http://www.camaros.net/forums/showthread.php?t=247050

Guy with a ZZ502 in his Chevelle, lives in Denver. Worked with Chris Straub to get him to 600HP with a 230/238 cam. Lots of lift. I don't think I'd go with a cam with more duration and less lift at our altitude. Looks like Straub has some experience working with the ZZ502 at altitude. Probably worth a free phone call or email ;)

chevynut
11-14-2015, 04:03 PM
Thanks Chad. Why do you say the guy with the Chevelle is in Denver? The post says he's in OH. :confused:

It does sound like it would be worth talking to Chris Straub and tell him what I have and what my goals are. And I agree that more lift here would help more than duration. Looks like one of his cams would be $545.

I found this stuff on Youtube:

"Cam specs...
.629 /.629 lift
281/293 Adv.
230/238 .050
154/158 .200
105/113 Centers
109 Sep

I had a custom cam designed by Straub Technologies, Edelbrock RPM Air Gap intake, ProSystems HP1000 carb, and had the heads milled .030" and a valve job. On the engine dyno it made 607hp and 620tq."

I calculate 16 crank degrees overlap on that cam. The Chevelle sounds pretty good. ;)

hutchenc
11-14-2015, 04:11 PM
Laz...I must have been reading another post about a different ZZ502 that Chris Straub was commenting on. Sorry about that, but there is a post somewhere out there where he did a ZZ502 in Denver.

$545 is an expensive cam, on the other hand...it's less than $300 more than an off the shelf grind. Optimized for a specific engine, it might be worth it depending on how much you're willing to spend. He might be able to recommend an off the shelf grind though.

Edit: Found the Denver ZZ502 thread here: http://www.chevelles.com/forums/showthread.php?t=145469&highlight=

That's a big cam. Probably a lot more than you'd want, but this one was for a drag car.

chevynut
11-14-2015, 04:16 PM
$545 is an expensive cam, on the other hand...it's less than $300 more than an off the shelf grind. Optimized for a specific engine, it might be worth it depending on how much you're willing to spend. He might be able to recommend an off the shelf grind though.

Yeah if he could give me a recommendation on specs maybe I could find an off the shelf cam that meets them. We'll see. It sure sounds like everyone thinks the cam in the 502 is tiny. :eek:

hutchenc
11-14-2015, 04:42 PM
It is pretty small. Just for comparison's sake, I run this cam in my '72 Camaro's 355. It will buck in 4th below 1400 RPM, but other than that it's really pretty street friendly (stock power brakes work fine).

http://iskycams.com/cart/index.php?main_page=product_info&products_id=1110

With 1.6:1 rockers, it has more lift than the ZZ502 cam has with 1.7:1 rockers.

chevynut
11-14-2015, 05:03 PM
With 1.6:1 rockers, it has more lift than the ZZ502 cam has with 1.7:1 rockers.

Okay, what am I missing?


Value Lift Int/Ext: .505/.530
ADV Duration Int/Ext: 272/282
.050 Duration Int/Ext: 225/234
Lobe Center: 112 -


With 1.6 rockers you get .808//848 lift at the valve with that Isky cam.

The 502 cam has .527/.544 lift. With a 1.7 rocker that's .896/.925 lift at the valve. :confused:

And the overlap at .050" on the Isky cam is only 5.5 crank degrees (9 degrees on the 502 cam). I assume it has a pretty mild idle?

hutchenc
11-14-2015, 05:13 PM
You need to divide the lift numbers by the rocker's ratio to get the lobe lift value. Then re-multiply by the new rocker value to come up with net valve lift numbers.

So, my cam's valve lift is 505/530 with 1.5:1 rockers. With 1.6:1 rockers, it's 538/565 lift. With 1.7:1 rockers (which are stock for BBC's I think), 572/600. Lobe lift is 336/353.

The stock ZZ502 cam with 1.7:1 rockers has 527/544 lift which means the lobe lift values for the ZZ502 cam are .310/.320. I hope that makes sense.

My point is that it is indeed a pretty small cam, especially for a 502ci motor. I really think more lift would help a good deal.

And yes, the idle is pretty mild. Here's a clip of it idling:
https://flic.kr/p/aKkaUr

chevynut
11-14-2015, 05:17 PM
Okay I'm learning lol. I thought the .505/.530 was the lobe lift, but in retrospect that would be a huge lobe. :)

I guess I was focused more on the math than what a nearly 1" lift valve would do. LOL ;)

It's good to do these comparisons because it really shows what I'm dealing with. Looks like I could use a lot more lift even if the duration and everything else was about the same.

hutchenc
11-14-2015, 05:36 PM
I think you might face some limitations on lift with those valve covers. Might look into that.

Also, I'm assuming that if you run more lift, say, closer to .600, you'll have to change valve springs.

Last, if you're looking at swapping to roller-tipped rockers, make sure they can tolerate the open pressure they'll see with bigger springs/more lift if you go that route.

I really enjoy this part of hot rodding...this is the fun stuff :)

chevynut
11-14-2015, 06:41 PM
Looks like it could snowball really fast. I don't want that to happen ;).

I don't know a lot about the valve springs they have in the engine but the GM part number is 12366989. According the the Chevrolet Big Block Parts Interchange Manual I found they're heavy duty springs good to .675" lift. ;)

Here's another article I found on modifying the 502.....

"Opening up the crate engine, then, should pay significant dividends. That seems to be the case with this 502, which jumped about 80 horses with the following upgrades:
* Cam changed from .527/.544 lift and 224/234 duration to .566/.566 lift and 296/302 duration, with a 110-degree centerline.
* Comp Cams 1.7-ratio roller rocker arms (stock does not include roller arms).
* Comp Cams #924 valve springs; dampened two-spring design with 115-pound seat load and a 322-pound open load.
* "Cleaned up" heads, including port-matching with intake manifold.
"The modifications simply allow the engine to push more air," says Martin. "They also allow the engine to rev a little higher, but not much. It's not an RPM motor."
Actually, it's not the valvetrain or reciprocating assembly that is the 502's effective rev limiter; it's the throttle body.

"Its limit is simply less than the engine's capability," explained Martin. "The engine would definitely make more power with a bigger throttle body."

http://www.superchevy.com/how-to/0408sc-ram-jet-502-engine/

markm
11-14-2015, 06:49 PM
My oval port 454 drag moter .595/.621 lift solid ran for years with stock L88 valve springs.

Rick_L
11-15-2015, 07:14 AM
"Opening up the crate engine, then, should pay significant dividends. That seems to be the case with this 502, which jumped about 80 horses with the following upgrades:
* Cam changed from .527/.544 lift and 224/234 duration to .566/.566 lift and 296/302 duration, with a 110-degree centerline.


You don't get something for nothing - if you get 80 hp from a cam change, you are going to lose the equivalent at low rpms.

They have their context screwed up, you can't run 296/302 duration @.050" on the street, maybe not even on the race track.

Straub is not going to give you a recommendation for an off the shelf cam, his business is custom grinds and that's what he'll steer you to, right or wrong.

You may be making too much of increased lift unless you have ported heads. Increasing the lift without changing the duration means harsher cam action, which means stiffer valve springs. At some point that also means wear and tear on the rest of the valvetrain.

chevynut
11-15-2015, 08:01 AM
They have their context screwed up, you can't run 296/302 duration @.050" on the street, maybe not even on the race track.

As far as I could tell they didn't say the duration was at @.050" so maybe it was "advertized" duration. I wondered about that myself. It's hard comparing cams when you don't have the full specs. I can't find the "advertized" duration for the 502 cam.

I'm not sure you have to lose anything to gain something. Like he said, the engine would benefit from a larger TB, and I don't think that sacrifices low end power.



You may be making too much of increased lift unless you have ported heads.

The 502 heads are CNC ported and flow well, from everything I've read. Not sure how much you could gain by doing more porting. Here's an article about that...

http://www.superchevy.com/how-to/68318-502-ci-engine-build/

Here's some actual flow numbers I found in a different article. The "before" is stock ZZ502 heads, and the "after" with some porting. They said the porting increased chamber volume from 110 to 117 CC. That seems like a lot, resulting in a drop in compression. Not going to do that. :)



Flow Numbers



Intake
Exhaust


Lift (inches)
Before
After
Before
After


0.2
138
149
119
122


0.3
193
218
145
153


0.4
233
278
168
170


0.5
272
306
189
187


0.6
299
331
202
201


0.7
318
347
210
216


0.8
327
359
230
226








Increasing the lift without changing the duration means harsher cam action, which means stiffer valve springs. At some point that also means wear and tear on the rest of the valvetrain.

Yes I understand that but the cam in the engine is pretty small, and the stock valve springs can handle more lift...a lot more. Also, I don't want to build a race engine, so any change would still be fairly reasonable, trying to maintain the streetability and reliability. I don't want to get to that "some point". ;)

Rick_L
11-15-2015, 10:25 AM
I'm confused, you say that the 502's heads are CNC ported, yet you post up two references to porting them. Which is it? Have you verified that the heads you have are ported?

On the lift/valve spring issue, the valve spring has more to do than accommodate lift without coil binding the spring. It has to control the valve action and keep the lifters on the lobes. More aggressive opening and closing rates mean you need more spring pressure.

The thing about all this is that as always there is no silver bullet and no clear easy cheap solution.

chevynut
11-15-2015, 10:45 AM
Rick, I might be wrong but I read somewhere that the 502 heads are CNC ported. I've not looked at them closely to verify. They are supposedly Edelbrock castings with larger valves in them. These stock zz502 parts are some very good quality parts. Rods and crank are forged, pistons are JE forgings. Valve springs should be no issue. Seem like they cheaped out on the stamped rockers.

chevynut
11-15-2015, 10:56 AM
I just checked and no, it doesn't look like the heads are CNC ported. Not sure where I read that but it was a long time ago and I may have misinterpreted it.

I also found some specs on the valve springs GMPP 12462970 ....

Dual springs
OD 1.514"
Pressure at installed height 140# @ 1.940"
Coil bind height 1.20"
Rate 368 lb/in (Per GMPP catalog)

2.25" intake and 1.88" exhaust valves are stainless steel with 11/32" stems.

Rick_L
11-15-2015, 04:55 PM
I'm sure the Edelbrock heads are available CNC ported, don't know about from GM.

Did you verify that you have Edelbrock heads? I thought those 520 GM crate engines had GM heads. And nothing wrong with that for the price. Edelbrock heads are not a killer deal, not in the same class as Brodix or Dart. They are very conservative. And for your car, you don't need Brodix or Dart.

chevynut
11-15-2015, 06:46 PM
Yes they have GMPP heads. My understanding is that the GMPP heads are made by Edelbrock and have the GMPP logo CNC machined into them. I've read that several places before. Apparently this casting isn't offered by Edelbrock with the 2.25" valves....or it didn't used to be.

I'm sure there are better heads on the market, especially for making the maximum power. But these heads are pretty good.

Five Seven
11-20-2015, 02:38 PM
Just curious if you are planning to upgrade your EFI unit to an HP. I am running a stock ZZ502 with MPFI/Vic Jr manifold and a holley HP system. It works well, the self learning feature is important in my opinion. One thing I would suggest when you have your engine apart is to inspect your lifters if that is possible. My valves were noisey as set by the factory and when I got around to adjusting them, found that one was collapsed (stuck compressed).

chevynut
11-20-2015, 04:40 PM
Five Seven, I plan to run the Commander 950 Pro that I have. Don't know if I plan to upgrade in the future. I'll check those lifters...thanks for the tip.

Do you have the stock cam in your ZZ502? How does it sound to you? This one sounds pretty good to me... :)

https://www.youtube.com/watch?v=LJ0EGOUsjHs
(https://www.youtube.com/watch?v=LJ0EGOUsjHs)

Watch this at 2:25 ;)

https://www.youtube.com/watch?v=96QB7VLnZ0o

Five Seven
11-22-2015, 11:30 AM
Great videos. I'm happy with how it sounds although I am running a temporary exhaust system. I'm curious to see how a full system with a crossover tames it down.

chevynut
04-17-2016, 08:11 AM
I thought I'd go back and re-visit my cam decision since I'm close to re-assembling the engine.

To review, the current stock cam in my 502 has these GM specs....

Stock 502 cam
.527/.544 lift
224/234 @.050"
110 degree LSA

I found some additional cam information on a Chevelle site where a guy supposedly measured the cam: http://www.chevelles.com/forums/13-performance/393792-zz502-cam-info.html

Cam # 12366543 measured

ID 224 @ 0.050 / adv dur 294*
ED 234 @ 0.050 / adv dur 304*
LSA 110
ICL 108
IVO 4 BTDC (- indicates ATDC)
IVC 40 ABDC
EVO 49 BBDC
EVC 5 ATDC (- indicates BTDC)
ECL 112
Overlap 9 (based on .050" duration)
I/Lift @ cam .310
E/Lift @cam .320

I calculate 79 degrees overlap using the advertized duration numbers, which is more than any of the cams below. It also has more lift than most of them. So this cam seem to me that it's not as "tiny" as everyone thinks it is.

Here's some specs for some other cams I've looked at and read about:

Comp XR282HR-14
.510/.520 lift
230/236 @.050"
282/288 advertized (Overlap 57 degrees)
114 degree LSA

Comp XR288HR-14
.520/.539 lift
236/242 @.050"
288/294 advertized (overlap 63 degrees)
114 degree LSA

Comp XM296HR (marine roller in article above)
.566/.566 lift.
242/248 @.050
296/302 advertised (overlap 75 degrees)
112 degree LSA

Crane 168671
.597/.610 lift
230/236 @.050"
292/298 advertized (71 degrees overlap)
112 degree LSA

It seems like I would benefit from a cam with a little more lift, but not any more duration. I don't know if the measured duration is accurate, but I have no reason to believe it's not. The cam does seem to have a fairly choppy idle, which I like the sounds of.

My valve springs can handle more lift without any problem. The XM296HR cam has more lift but I'm concerned about the duration at .050". It must have steeper ramps than the 502 cam. What makes it a "marine" cam???

I guess I need to look at other suppliers and see what they have. I may talk to Chad's guy and see if he has any recommendation for my engine at this altitude.

markm
04-17-2016, 08:53 AM
My 425 HP 396/427 cam has .520 lift and 244 dur.@.050. What's wrong with duration it s what makes power.

Rick_L
04-17-2016, 02:16 PM
Having a lot of "advertised" duration relative to the .050" duration is typical of a GM factory high performance cam. What that does is bleed off a lot of low rpm cylinder pressure and give you a big lope at idle. It also gives you a little bit gentler valve opening/closing action and doesn't require as much valve spring. This relative to the aftermarket cams shown. The aftermarket cams should have a broader power curve and might even get a bit better fuel mileage.

Yes, duration will get you more power, but you have to run more rpm to get the power. The differences in lift between all these cams is not a big deal. You need to see an .050"-.075" difference in lift to make a difference with this engine.

Personally I don't think you'll ever a see a seat of the pants difference between all the cams listed considering everything else about the combination, so I wouldn't screw with it. To see a difference, you need more duration and lift, and then you'll be giving up some street manners and mileage. You will also be fighting the tuneup a bit more to get it right.

markm
04-18-2016, 08:01 AM
Anyone who pays any mind to advertised duration specs is lost, the L-82 cam in my Z28 is advertised @346, but when measured at .050 its only 222.

chevynut
04-18-2016, 09:08 AM
Having a lot of "advertised" duration relative to the .050" duration is typical of a GM factory high performance cam. What that does is bleed off a lot of low rpm cylinder pressure and give you a big lope at idle.

That's what's been puzzling to me but I think you answered my question. The COMP guy at SEMA said the guys with 502's complained the idle wasn't lopey enough. I think it's pretty lopey that's why I wondered why so many people think the cam is so small. I guess the long adv. duration explains that.


Yes, duration will get you more power, but you have to run more rpm to get the power.

I don't want to do anything to lose torque on the low end (2500-4000) but would like to gain some on the high end (4000-6000) if possible. From what I've read my 1000 CFM TB will help. But most of the 502 tests I've seen have been with a carb.


The differences in lift between all these cams is not a big deal. You need to see an .050"-.075" difference in lift to make a difference with this engine.

The "marine" cam is getting there, with a .042" intake lift increase. It has a little less overlap based on advertized duration (75 vs 79 degrees) but a lot more (21 vs 9 degrees) based on the .050" duration. I'm assuming the advertized duration is what determines the lopiness and driveability of the cam.


Personally I don't think you'll ever a see a seat of the pants difference between all the cams listed considering everything else about the combination, so I wouldn't screw with it. To see a difference, you need more duration and lift, and then you'll be giving up some street manners and mileage. You will also be fighting the tuneup a bit more to get it right.

I thought more lift would help due to the altitude here, as Chad was commenting on. I don't want to sacrifice "street manners" and I think the 502 cam sounds great at idle. I also don't want to replace more of my valvetrain because things snowball fast.

The Comp marine cam above gained 80HP but that was also with some head work which I don't want to get into.

Here's an article about the Comp XR288HR. It's not the cam I posted above, but it has the essentially the same specs except the LSA is 110 instead of 114 on the XR288HR-14. Obviously a couple of typos here: http://www.trucktrend.com/how-to/engine/0404st-502-chevy-big-block-buildup/

" Comp Cam's answer to GM's cam choice came in the form of an Extreme Energy XR288HR hydraulic roller camshaft. This profile would really wake up our engine, while still maintaining a smooth idle and driveability, because the engine would still make enough vacuum at idle to operate a truck's power braking system. Another bonus with this camshaft is that there isn't any need to re-adjust the valve lash after installation because of the hydraulic roller lifters used. The XR288HR specs out like this: At 0.50 lifter rise, the intake has a duration of 0.236 and the exhaust, 0.242; gross valve lift occurs at 0.521 inch for the intake valves and 0.540 for the exhaust; and lobe centerline is 110 degrees."

"With these minor alterations to the top end of the engine, we were able to push the big Rat motor to build more than 570 hp and 620 lb-ft of torque. This was an increase of 37 hp and 52 lb-ft of torque over our baseline dyno testing. More importantly, though, the engine was now pumping out more torque across the board, with numbers more than 600 lb-ft from 3,800 rpm to 4,800 rpm. "

I've seen articles showing stock crate 502s getting anywhere from 500HP to 530 HP in stock form, depending on the dyno and specific setup.

Here's an article on the Crane cam I posted above....they got 55HP more with it and more torque with a broader torque curve. It has just slightly more duration (230/236 @.050") but a lot more lift (.597/.610) with overlap a bit less than the 502 cam at advertized duration and exactly the same at ,050". This is the kind of result I'm looking for, but don't know if it's feasible with my valvetrain.


http://www.superchevy.com/how-to/engines-drivetrain/1412-how-to-install-a-crane-cam-on-zz502-little-bit-o-boost-part-2/

http://image.superchevy.com/f/81241731+w640+h640+q80+re0+cr1+st0/cam-swap-graph.jpg

Chevy says the springs I have are good for .675" lift, but this article says they're weak. They have the highest seat load of any spring listed in my GMPP catalog (2001 version) at 140 lb at 1.94" but the spring rate is 368 lb/in versus 450 lb/in for the LS-6 454 springs. They show only 105 pounds seat load at 1.88" installed height for the LS-6 springs. The Crane springs they used were 200 pounds at 1.90" and a spring rate of 475 lb/in. At .600 lift they had 500 pounds of load. And that article shows how everything snowballs when you start changing stuff. :cry:

"We tested the springs and weren't surprised when the results were barely 150 pounds of load on the seat. These are very low numbers for a big-block Chevy with heavy valves. Westech's Steve Brule says his experience is that a minimum of 200 pounds of seat load is required to keep control of the valves at higher engine speeds."

markm
04-18-2016, 09:33 AM
I'm assuming the advertized duration is what determines the lopiness and driveability of the cam.

It means nothing, that why the standard of measuring at .050 lift was developed in the late 70s by Harvey Crane if my memory serves me correct.

Rick_L
04-18-2016, 10:16 AM
Lots of advertised duration will affect the idle. But if it's big with respect to the .050" duration, it doesn't affect the power level. I do think it matters to driveability too.

Just because a valve spring is capable of having the valve open to .675" lift doesn't mean that is has the spring force required to control the valve motion. Two separate deals. High rpm means you need more spring force.

You are reading ads for cams that exaggerate their characteristics, though they are disguised as factual magazine articles. In general, you need to see the .050" duration change 10 degrees to see a meaningful difference, and you need to run 500-700 more rpm.

I don't think you'll find the 1000 cfm throttle body will make much difference. In fact it will fool you because as it first opens it's going to flow a lot more air for a give pedal movement than a stock one - leading you to think you did something when in fact all you did was change the throttle opening for a given amount of pedal.

If anything, you don't need as much lift at elevation because the air is less dense.

chevynut
04-18-2016, 11:22 AM
Here's an excellent technical article I found on cams...by a well-known engine expert David Vizard.

http://www.hotrod.com/how-to/engine/0607phr-camshaft-basics/

I found these excerpts interesting.....

"What dictates the cam's success in the quest for maximum area under the output curve along with highest peak torque and horsepower is not (as is so often assumed) the duration involved. The most important factor is actually the overlap and the Lobe Centerline Angle, often referred to as the LCA.

"Assuming we are choosing a cam for a streetable engine, how much overlap can we use before it becomes a problem? The answer here is that it depends on the valve sizes in relation to the cylinder displacement. If the heads have small valves in relation to cylinder cubes, then the amount of overlap we can use is significantly more than the same cylinder with much larger valves. For instance, a 500-inch big-block Chevy can tolerate not only more overlap, but a much bigger cam because the cylinder heads are so under-valved for the displacement."

"If maximum torque and power along with the biggest area under the curve is the target, then only one LCA will do the job, and it has to be the one the engine wants, not one you or someone else doing your guessing for you arbitrarily decides is the one needed."

"This forces us to the conclusion that for a given duration, there is only one optimal opening point and one closing. This, in turn, means, within a small window, only one LCA gives optimal results. If the LCA is spread to preserve the idle and vacuum, the price paid is reduced torque and hp. We should have gone to a shorter cam on the correct LCA, as it would have produced better results!

"The moral here is that if the cam had been selected on the basis of overlap and LCA first, then the duration would have been decided by these two factors, not some arbitrary decision on the part of the hot rodder."

"Assuming the compression ratio remains constant, longer duration just moves the torque curve up the rpm range. Peak torque itself usually only increases a minor amount. The additional hp comes from the fact that the torque delivered happens at a higher rpm and power is directly proportional to torque times rpm."

"As can be seen from the results, the peak power output from each combination was near identical, but the shorter-duration, high-lift combo made power at less rpm because it produced more torque, especially at low speed."

"Higher-ratio rockers can spread the engine's required LCA. This means that if the existing cam has too wide an LCA, as is so often the case, bolting on a set of high-ratio rockers can pay a handsome dividend. On the other hand, if the LCA was such that the overlap triangle was optimum, installing a higher-ratio set of rockers can drop output rather than increase it. My own tests have indicated, within the ratio range of 1.5 to about 1.9:1, that for every 0.1 ratio increase on the intake, the LCA needs to be spread by 0.75 to 1 degree. As for the exhaust, we find that it is relatively insensitive to valve acceleration but is sensitive to duration. For this reason the rocker ratio used on the exhaust is best kept about 0.1 to 0.2 of a ratio lower than the intake ratio."

"during the mid 1980s GM began research on the application of a design known as the "beehive" spring. As its name suggests, this spring is wound in a beehive form. With each coil getting progressively smaller, this spring has no clear-cut resonant frequency. As soon as it starts to resonate at a particular frequency, the resonant frequency changes. Result: Spring surge is, in almost all applications, reduced to levels bordering on insignificant. The beauty of the beehive spring is that it uses its delivered force far more effectively than a conventional parallel-wound spring. It needs far less of its delivered force to control its own motion, so this leaves more to control the valvetrain. This means less overall valve-spring loads while delivering more rpm. Our spin tests on a street roller cam showed an rpm increase from 5,950 to 6,900."

"Exactly what LCA does an engine need for optimal results? The bottom line is that it's all related to how big a cylinder the intake valve has to feed. The bigger the cylinder in relation to the valve, the tighter the LCA needs to be, and vice versa. That is the main factor. Additionally, but to a lesser extent, we also find that as the compression ratio goes up, the optimal LCA gets wider. "

So looking at all this I took this table and calculated my 502's displacement vs valve diameter at 28. It says I need an LSA (LCA) of 100 degrees?? Then why did the Comp guy recommend a cam with 114 degrees LSA instead of 110?

http://www.hammertime.us/gallery/albums/images/LCA_Determination.jpg


http://www.hammertime.us/gallery/albums/images/overlap_estimator.jpg

chevynut
04-18-2016, 11:45 AM
Here's a couple more Vizard articles with similar info:

http://www.stockcarracing.com/techarticles/scrp_0612_lobe_centerline_angles/
http://www.hotrod.com/how-to/engine/cam-lobe-centerline-angle-tech/

"A cam ground on a wide LCA has less intake valve opening at TDC, so reaches peak opening later in the induction stroke. This means as the piston accelerates down the bore it creates a greater discrepancy between the flow delivered by the valve and the flow required by the cylinder. Put simply, this is because during the first half of the induction stroke the valve is not as far open when a wide LCA is used as it is with a tight one."

markm
04-18-2016, 01:10 PM
Isn't he the guy who wrote those HP books How to Hot Rod SBC & BBC and How to rebuild SBC, I still have them in my library of resources.

hutchenc
04-18-2016, 01:11 PM
I'm willing to bet that Comp Cams' "experts" know very little and probably base their recommendations off of what CamQuest tells them. I'd rather get it straight from a person who really knows cams.

I'd call Mike Jones or Bullet Cams and see what they say. If you swap cams for a custom grind, I'd be prepared to switch valve springs, just a hunch. Generally speaking, the wider LSA will make the engine idle more smoothly and it'll give EFI a better and more stable vacuum signal for tuning so that may have factored into his 114 LSA recommendation. At some point you need to decide whether you want max power (which is what Diavid Vizard is writing about) or something more streetable. Along the max power<---->towing spectrum, I imagine you want something in the street performance area, but not street/strip or anything higher. I don't know anything about big blocks, but I do know that you can run less LSA on a bigger motor. The cam in my 420 is on a 108 LSA btw (and according to that chart, I should be on a 104...I wouldn't take it at face value for a street application). It's idle is fairly stable, not too choppy.

chevynut
04-18-2016, 02:08 PM
As I said, I'd like to see something that would give me a torque curve more like the one I posted above using the Crane cam. ;) This is a typical stock RJ502 dyno run but I've seen slightly higher numbers:

http://www.chevrolet.com/content/dam/Chevrolet/northamerica/usa/nscwebsite/en/Home/Vehicles/Performance/Engine_Detail/Big_Block/ZZ502_502_Deluxe/dyno-chart-zz502-deluxe-482x244.jpg
http://www.pswired.com/misc/pacaudio/saturnstyl/dyno10001.jpg


I don't want too rough of an idle but it seems like I could use more lift. The lift numbers on the other cams just seem small. Vizard says that duration only pushes the torque curve to higher RPM, and really doesn't increase torque. So it seems like lift is the key to make more torque and the Crane cam kinda confirms that to me. The stock 502 cam has higher lift than most of the others, along with good duration numbers and a 110 LSA. Overlap of 79 degrees surprises me considering it's street engine.

Rick_L
04-18-2016, 02:57 PM
I don't know how well Vizard's recommendations on lobe centers and overlap hold for street engines, but they seem to make sense for race engines. I can tell you that his recommendations for race engines seem to follow what I know and learned with them. In short, as my race engines got better flowing heads with bigger intake valves, the lobe center angle increased and the overlap decreased. As a side benefit, this allowed shallower valve reliefs in the piston domes which increased the compression ratio. Conversely, when I ran cast iron heads limited by the rules, we "crutched" them with 106 degrees lobe centers and lots of overlap.

So if you want to change something, consider changing the lobe center angle. What LCA does Vizard's stuff recommend for a street engine like yours? Did your article make a definite recommendation? I know that LS engines seem to run wide lobe centers.

hutchenc
04-18-2016, 08:04 PM
I think you could run a good deal more lift Lazlo...it may very well mean you need to change your valvesprings though. A cam with more lift but not much more duration means you'll need a higher spring rate to handle the steeper ramp of the cam lobe. I'm running .600/.555 lift on the with my 420. No reason a BBC can't handle the same thing. Picking up a little bit of duration, but a lot of lift would probably get you what you want power-wise and not ruin the streetability of the car.

chevynut
04-19-2016, 09:37 AM
Just because a valve spring is capable of having the valve open to .675" lift doesn't mean that is has the spring force required to control the valve motion. Two separate deals. High rpm means you need more spring force.

I understand that, but I don't plan to push the engine past 6000 RPM. I see guys replacing the springs in some of these cam tests, but they don't prove that the stock springs will or won't work up to that level. In fact, in the Truck Trends article they kept the stock 502 springs with the XR288 Comp cam. The stock springs seem pretty stout to me compared to many of them I've looked at.


I don't think you'll find the 1000 cfm throttle body will make much difference.

I've read several articles that say the stock dual 48mm TB (635CFM) is choking the engine and that a larger TB will help. To me it's like trying to run a 650 Holley on a 502...we know that's not a good idea. ;)


If anything, you don't need as much lift at elevation because the air is less dense.

Seems like that's precisely why you DO need more lift. There's less pressure difference so you need a larger opening to get more air in the cylinder. Reagrdless, it seems like a bigger opening flows more air, whether "thick" or "thin". Here's what Chris Straub says about it:

"With an altitude build you want a head that flows air very quickly at low lift. You want to get as much air in as you can and shut the valve. Cam profile needs to be moderate on duration and to the aggressive side with lift. This will get you the best performance with engines built for elevation.

Read more: http://www.corvetteforum.com/forums/c3-tech-performance/3720155-high-altitude-engine-build.html#ixzz46I6OCyun

chevynut
04-19-2016, 10:57 AM
Thanks for the discussion guys. Before I started this I knew very little about camshaft design (never even heard of LSA), but I've learned a lot here.

I looked at all the Comp cams for my engine, and just recently looked at several Lunati cams as well as some Crane cams. I noticed a lot of the "hot street" cams they list are actually smaller than mine in both duration @.050" and lift. In fact, most of the street/strip cams that Lunati sells are smaller than my 502 cam.

I don't want to change duration much because I don't want to lose low end torque and don't really want to shift the torque curve upward. I assume that means I need to keep close to the same duration at .050" as I have now, perhaps a bit more. So something in the 224-230 range on intake and 236-240 range on exhaust seems like a target to shoot for.

Based on everything I've read I think I need an LSA between 110 and 114, with 114 being better for EFI. It so happens that all the cams I've looked at fall in that range. A wider LSA is better for EFI as Chad mentioned, due to the better vacuum signal. The current cam is 110 LSA and it seems to work well. But I also think that vacuum signal varies with overlap, not only LSA, correct?

I think based on idle quality, I want a cam that sounds like the 502 cam, so I probably want similar overlap (79 degrees) at advertised duration. So something in the 65-75 degree overlap range seems like the best choice. Also it seems like I should be shooting for similar overlap when looking at duration at .050", which is now 9 degrees. So perhaps 7-11 degrees there would work.

As far as lift, I think it could use more, and the articles I posted seem to suggest that it will help, as well as Straub's recommendation to be aggressive on lift at altitude. I think something in the .575-.610 (intake) range seems like a good place to be. Not sure how that affects my springs, because I haven't seen anything that says when your springs aren't good enough and what the limit is. I understand the need for higher spring loads with aggressive cams, but nothing I have found gives me an number to go by at some given lift for a given engine.

Comp recommended their XR282HR-14 to me at SEMA, but I don't see how it makes any sense. It has a bit more .050" duration at 230/236 versus 224/234, and lower lift of .520/.540 versus .527/.544. It seems like that's going in exactly the WRONG direction. The main difference is the 114 LSA versus 110. The overlap at adv. duration is 57 degrees versus 79 with my current cam and overlap at .050" is 5 degrees versus my current 9. It seems to me that this cam buys me nothing.

So here's a few cam possibilities I've picked out:







.05
.05
.05
adv
adv
adv



.............................
lift I
...lift E
LSA
durI
durE
olp
I
E
olp










stock ZZ502...........
0.527
0.544
110
224
234
9
294
304
79





Comp XR288-14.....
0.520
0.539
114
236
242
11
288
294
63





Crane 168761.........
0.597
0.610
112
230
236
9
292
298
71





Lunati 20010722.....
0.600
0.600
110
231
239
15
282
290
66





Lunati 20010349.....
0.578
0.585
112
232
242
13
290
300
71





Lunati EFI 20010666
0.554
0.575
114
226
236
3
285
295
62





Lunati EFI 20010667
0.554
0.575
114
230
240
7
289
299
66





Lunati EFI 20010668
0.575
0.575
114
234
244
11
293
303
70





Lunati EFI 20010669
0.629
0.612
114
234
244
11
293
303
70



In the magazine article tests they gained 57 HP and 35 ft-lb with the Crane cam above but I question their low stock torque numbers at only 539 ft-lb versus GM spec (and verified many times) at 567. That cam has fairly close duration and overlaps specs as my current cam.

In the magazine article tests they gained 37 HP and 52 ft-lb with the XR288HR cam, which is the same basic grind as the one above but with a 110 LCA instead of 114. They reported a peak torque of 620 and HP of 570. The peak torque RPM shifted DOWN a little and the pea kHP RPM didn't change which seems strange given the longer duration.

Would the Lunati 668 or 669 EFI cams be too much for what I'm trying to do? I don't want to get too radical but I feel there's some power to be had.

chevynut
04-19-2016, 11:00 AM
Regarding valve springs, my springs have 140 pounds load at installed height. At .600" lift they should have 361 pounds of load. How much do you need to control a 2.25" valve at 6000 RPM?

chevynut
04-19-2016, 11:46 AM
I found this chart that I thought was interesting. It doesn't really have all the info I need, but you can infer some things from it...

http://www.hotrod.com/how-to/engine/hrdp-1011-what-you-need-to-know-about-valvesprings/

http://image.hotrod.com/f/30905719+w660+h495+cr1/hrdp_1011_04_o%2bwhat_you_need_to_know_about_valve springs%2bgeneric_valvespring_selection_guidelines .jpg

Looks like a BBC with a hydraulic flat tappet cam with 220/226 duration and 525/.530" lift running at 6000 RPM needs around 130 pounds on the seat, and around 320 pounds open. They don't say what the valve size is.

A BBC with a hydraulic flat tappet cam with 230/236 duration and .533/.556" lift running at 6500 RPM needs around 140 pounds on the seat, and around 345 pounds open.

A BBC with a hydraulic roller with 230/236 duration and .612/.607" lift running at 6500 RPM needs around 170 pounds on the seat, and 415 pounds open.

None of these say what the valve size is, or other specifics. I assume duration matters because it affects ramp speed. Why does a roller cam need more spring, is it because of the lifter weight or are the profiles more aggressive? I read an article that said you can get the same valve lift profile with a flat tappet cam as a roller.


So I wonder how much of a cam I can run with my stock springs using a 2.25" intake valve at 6000 RPM....or conversely, what spring pressures would be needed to run around 230 duration and .600 lift with a 2.25" intake valve. I assume you only need to be concerned about the intake side since the exhaust valve is smaller and lighter so I don't understand why the chart shows both intake and exhaust specs.

markm
04-19-2016, 12:32 PM
I am starting to understand why your car is not done you over analyze every detail.

chevynut
04-19-2016, 12:51 PM
Some more stuff...

"Hydraulic Roller Cams Hydraulic roller (HR) cams require higher pressures to control the inertia of the heavier roller lifters and the faster acceleration of valve train components allowed by the use of the roller follower. Pure street small blocks should have 260-300lbs open pressure. For performance use, aim for 300-350lbs open. Racing small blocks that regularly see 6,000+rpm need over 400lbs open pressure. At these pressures, premium valve train components including a “billet” type cam are required. Even with these components, there will be reduced service life and the consequent need for more frequent parts inspection and replacement. Big blocks need closer to 300lbs open pressure for street driving and 350-375lbs is preferred for performance use. A racing big block needs 450lbs. As with small blocks, premium components including lifters are needed at higher pressures and rpm. As with solid lifter cams, seat pressures should be in the range of 105-125lbs for small blocks and 115-130lbs for big blocks for performance street cars. Blower cars and race cars will need higher seat pressures."


I can't find any good guidance on this subject anywhere. Everything I read says use the "recommended" spring loads. Who recommends them?:confused:

Seems like someone should be able to come up with a chart or software where you enter the wight of your components and cam specs and get a reasonable answer.

chevynut
04-19-2016, 12:55 PM
I am starting to understand why your car is not done you over analyze every detail.

It's better than following your advice and sticking in a cam that doesn't work. LOL! You said you need more duration to change anything...all it does is shift the torque curve higher, and that's not what I want to do. Trial and error isn't the way I typically do things. I want the parts to work together the way they're supposed to to make a reliable setup. If you don't have any useful input on the subject, or any other subject, then STFU.

55 Rescue Dog
04-19-2016, 01:04 PM
It's better than following your advice and sticking in a cam that doesn't work. LOL! You said you need more duration to change anything...all it does is shift the torque curve higher, and that's not what I want to do. Trial and error isn't the way I typically do things. I want the parts to work together the way they're supposed to to make a reliable setup. If you don't have any useful input on the subject, or any other subject, then STFU.
You probably already have the perfect cam, but you will never know, after you have blown a bunch of "extra money" on a different cam you don't even need.

Rick_L
04-19-2016, 01:07 PM
Your post #60 says it all. You make a convincing argument NOT to change the cam. Read it back to yourself.

As you say, a roller lifter is heavier than a flat lifter, especially the hydraulic ones. This requires a bit more spring force, all else equal. The other thing is that a roller cam DOES allow quicker valve action, contrary to your statement. With a roller cam, you can grind it with a local concave profile, and the roller will follow it. This potentially can be used for very quick valve opening. A flat lifter requires a cam profile that is convex so the there is only 1 line of contact. Also with a flat tappet you can't have the cam contact the edge of the lifter. We used to use a lobe like this on race engine, called it the "peanut lobe" because that was its shape. Now, a street engine won't use something that radical, but you can definitely get away with more action when you use a roller, and the cam companies do take advantage of that.

markm
04-19-2016, 01:39 PM
Actually I find cam choice has too many personal preferences and variables associated with it and its about like trying to advise someone what to look for in a wife.

55 Rescue Dog
04-19-2016, 02:50 PM
If you really want to make bragging rite power, even at high altitude, why not just blow it?

chevynut
04-19-2016, 03:14 PM
Your post #60 says it all. You make a convincing argument NOT to change the cam. Read it back to yourself.

I did? I'm looking for 50 or so "easy" HP and more torque in the 2500-4000 range and it looks to me like at least a couple cams fit that goal. All I want to do is move the torque curve upward like the dyno graph I posted. I don't want to shift the torque curve higher.

I'd spend another $200-400 or so on an upgrade if it made a noticeable difference and didn't destroy streetability.

I think I'll give Lunati a call and tell them what I'm looking for, and have them tell me if it's reasonable.

chevynut
04-19-2016, 03:15 PM
If you really want to make bragging rite power, even at high altitude, why not just blow it?

The car is already built and I'm not looking for a 200+ HP gain. The intake stuff is fabricated. I'm not taking that step now. The next one will be supercharged.

chevynut
04-19-2016, 03:20 PM
Actually I find cam choice has too many personal preferences and variables associated with it and its about like trying to advise someone what to look for in a wife.

That's the way it was in the 60's when people didn't understand cam design. Now it's more of a science than an art. Get up to speed.

Rick_L
04-19-2016, 03:45 PM
If cam selection is so straightforward, why are there 73 posts in this thread with you asking a LOT of questions? Just sayin'.

chevynut
04-19-2016, 03:55 PM
The real issue I'm trying to address here is I've read several places where people say the stock 502 cam is "small" and it's been said here too. It never sounded "small" to me and it's "bigger" than a lot of them being sold for street performance.

So with that in mind, it looks like there's still room to improve the cam specs and gain some performance, cheap, especially considering my altitude. I probably won't do it for a 10-20 HP or 10-20 ft-lb torque gain...that's only 2-3%. As I said, I want to see around 550 HP and 600 TQ if I do it at all.

The valve springs and valves are some of the best sold by GM, probably made by others. The aluminum heads are made by Edelbrock. I shouldn't necessarily have to change lifters, pushrods, valves, or springs to use a bigger cam based on what I've researched, but some of that isn't very clear. I don't want to unnecessarily overload the components with too heavy springs for 6000 RPM. I am planning to change to roller tip rockers anyhow since they apparently fit under my valve covers. I just think they have to be better than stock.

I'm not too hung up on doing this, but now is the time to decide and I want to make the right decision so I don't regret it later....either way.

chevynut
04-19-2016, 03:56 PM
If cam selection is so straightforward, why are there 73 posts in this thread with you asking a LOT of questions? Just sayin'.

Probably because I don't understand all the parameters, but there are those who do. Apparently it's nobody here. ;)

markm
04-19-2016, 03:59 PM
That's the way it was in the 60's when people didn't understand cam design. Now it's more of a science than an art. Get up to speed.


I have bought cams for my 55,56,4 Camaros and 1 Corvette and am happy with performance on all of them, besides I am not the one posing the questions. Too bad you don't have automatic so we could talk torque convertors and stall speeds.

Rick_L
04-19-2016, 04:02 PM
My recommendation to you is that you have a bunch of comments and have done some other research. Make a decision and get on with it. The only way you are going to get any better on this is to actually do it and get the experience. Then you can decide whether you made the right call and can use that to either modify what you have or apply your experience to the next one.

I learned a long time ago that once you get anywhere near the right cam, all the other similar choices really don't matter. There's not a whole lot of power in nit picking camshaft decisions.

chevynut
04-19-2016, 04:08 PM
Here's what I think I've learned....;)

Increasing duration doesn't increase torque, it just shifts the torque curve upward.
Increasing lift increases torque, and helps at high altitude.
.050" duration doesn't really tell how "lopey" the cam is at idle.
79 degrees overlap is a lot. :eek:
.050" overlap and overlap based on advertised duration differs a lot.
A wide LSA increases engine vacuum and decreases overlap for better idle.
Big engines perform better with a narrow LSA (if max power is the goal).
A narrow LSA moves torque downward in RPM and increases maximum torque but narrows the torque band.
A wide LSA moves torque upward, decreases torque, and widens the band.


So regardless of what I end up doing with my 502, I've learned a lot. Maybe I should have started a new thread on "Cam Design" instead of putting this all here. :) :)

hutchenc
04-19-2016, 04:16 PM
Ahh the pitfalls of asking a question like this on a forum. I'm no expert, but I know that picking a cam for our altitude isn't the same as doing it at sea level and that is lost on most people because they don't live at altitude.

So, like I said, pick up the phone and talk to someone who does know. When I had Mike Jones spec out my cam, he increased the lobe lift on the intake for precisely the same reason Chris Straub said...a bigger intake charge because we have much less air density up here. He also lowered the exhaust lobe lift and slowed the lobe down a bit in terms of duration.

Not many off the shelf grinds are going to be optimized for altitude. Probably not one actually.

The other thing, outside of a custom ground cam that I would consider is simply running a higher ratio rocker arm to increase the lift. You mentioned changing those anyhow...why not go to a 1.8:1 while you're at it and maybe leave the cam alone altogether? Not the perfect solution, but inexpensive and pretty easy.

Troy
04-19-2016, 05:42 PM
Just go get a 3/4 race cam and be done with it!!!! LOL:)

Rick_L
04-19-2016, 05:48 PM
Big engines perform better with a narrow LSA (if max power is the goal).
A narrow LSA moves torque downward in RPM and increases maximum torque but narrows the torque band.
A wide LSA moves torque upward, decreases torque, and widens the band.

I think you've generalized way too much and have come to some incorrect conclusions.

Big engines are less sensitive to LSA, and certainly don't necessarily need small LSAs.

A small LSA doesn't move the torque curve downward. It does make it narrower. The rpm where the best torque is made is dependent on duration.

A wide LSA doesn't move the torque curve upward. It does make it wider.

A wide LSA does make idle tuning easier. That's why an LS7 can idle at 500 rpm and make good power up to 6000 rpm.

Vizard explains that the ideal LSA for a given combination is dependent on intake flow/intake valve size relative to engine size. If the intake size/flow is compromised for whatever reason, then narrow LSA is probably in order. RPM is a factor here too. I.e., how big does the intake valve need to be for a given engine size/rpm limit?

chevynut
05-03-2016, 08:02 PM
Big engines are less sensitive to LSA, and certainly don't necessarily need small LSAs.

Vizard says otherwise as I posted before.


A small LSA doesn't move the torque curve downward. It does make it narrower. The rpm where the best torque is made is dependent on duration. A wide LSA doesn't move the torque curve upward. It does make it wider.

COMP Cams says otherwise:

http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx



Vizard explains that the ideal LSA for a given combination is dependent on intake flow/intake valve size relative to engine size. If the intake size/flow is compromised for whatever reason, then narrow LSA is probably in order. RPM is a factor here too. I.e., how big does the intake valve need to be for a given engine size/rpm limit?

Vizard says that ALL big cubic engines, like BBCs, are under-valved. So a narrow LSA generally helps increase power.

markm
05-04-2016, 01:01 PM
I have ran with hundreds of guys over the past 40 some years on the street and strip and have yet to see anyone make such a big deal out of cam selection. Maybe its a show car thing and I just don't understand.

chevynut
05-04-2016, 02:45 PM
So why do you bother reading any of this if you don't understand? Just go away if you don't understand that I'm trying to pick a cam for a particular application and goal in mind. Unlike you, I don't just stab a cam in and call it good and if the car flops just try another one. I want to understand what makes them work for my application. You said more duration.....that shows what you know. LOL! Not one cam manufacturer I've talked to is suggesting significantly more duration. You're so stuck in the 60's that nothing you say matters today anyhow.

It's funny how you have never shown any pics of your cars or do anything to them that you post here. All you do is criticize what others do and tell how your stuff is supposedly better yada, yada. I'll bet your car is a total hacked up POS and you're too embarrassed to show it.

Rick_L
05-04-2016, 03:46 PM
You can keep your stock cam and make up what you want for the hand lettered show display! No one will ever know.

markm
05-06-2016, 06:47 AM
Last time you stated this BS Cnut I posted a picture of my 56 and 67 SS 350 sitting in the staging lanes at the dragstrip, or how about my 55 link at the KKOA drags. Now thats two places that your show car will never see. Hardly a day goes buy that someone does not call or ask me for advice on such matters.

55 Rescue Dog
05-07-2016, 04:30 PM
You probably already have the perfect cam, but you will never know, after you have blown a bunch of "extra money" on a different cam you don't even need.
After over 141 posts on the subject, here was your answer to the best cam for the money. Just run it and see!