Freshening up my Ramjet 502

[chevynut]

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]

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]

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]

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]

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]

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]

Just throw a 3/4 race cam in it and it'll go like a raped ape!!!

[chevynut]

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 .

[chevynut]

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??? 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]

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/coverag...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.