Freshening up my Ramjet 502

[chevynut]

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]

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]

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


Watch this at 2:25

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

[Five Seven]

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]

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-p...-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]

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]

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]

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]

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/eng...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/eng...-boost-part-2/



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.

"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]

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.