200 hp

[enkeivette]

My Vette feels like it has 200hp. What, the, fuck??

I replaced the intake manifold gaskets because it was seeping oil. Took the carb apart and cleaned it. But the car has a rough acceleration now.

From low to mid rpm it feels almost like its either super rich, or Im missing fire in one cylinder. But the AFR checks out. And it literally feels like Im down 400hp, Sooo what the fuck?? Help me. Im a yuppie now, forgot how to tune.

[94cobra69ss396]

Did you do a compression test? Also check the plugs because if it was pulling from the lifter valley it would have been running lean and may have burned a plug.

[Vettezuki]

If it's not missing, but way down on power, sounds like lost compression as first guess. Any signs of blow by, consuming oil, typical shot rings kind of stuff?

[enkeivette]

Ok. Ill check the plugs and do a compression test. Maybe I just fucked up the intake manifold gasket install. Ug.

Doubt the rings are bad. They have about 2k miles on them.

[enkeivette]

The HGs on the other hand have been reused and copper sprayed 4 times now. Might have a leaky HG. But even with my last dyno run leaking 8 psi through my HG it still made over 400 whp. This feels like L48 slow.

[Shaolin Crane]

You can be down a cylinder and have AFR check out. My last fuel system issue I lost two cylinders on each side and the AFR still read normal. If you have a laser temp fun check header primary temps.

[enkeivette]

FUCKIN BALLS my Vette's fast. I forgot what it was like to drive that car.

I did a compression test, cylinders checked out, all 100-110. But 4 of the spark plugs were super oil fouled. (From when my intake was sucking oil in from the lifter valley). I changed all the plugs, and woah... Smoother idle, touchy throttle, crazy hp and no rough accel.The left exhaust bank smoked for the first 10 mins burning the oil caked in those cylinders.

I put the hammer down fast at about 45mph and almost got sideways. Btw, what is the lowest PSI I can run 19" low pro tires at? I'm at 17 now.

[94cobra69ss396]

I hope your gauge just reads low because 100-110 is really low. The Explorer cold cranks 150, the Cobra cranks 170-180 and if I remember correctly the Chevelle cranks 210. Compression ratios are 9.07, 9.28 and 12.2 respectively.

[Shaolin Crane]

Mine cranks cold in the 150 range too. 9.36:1 compression.

[Vettezuki]

There's kind of a a lot to engine cranking pressure, but agree 100-110 sounds pretty low. I know he has a big cam and its a stroker, but I don't think his CR was that low.

http://www.not2fast.com/turbo/compression/cranking_pressure.shtml


PS 17 PSI on low pro street tires feels like asking for trouble, but I have no knowledge or data about it.

[Vettezuki]

PS Adam's Vette is still the fastest car I've been from a roll. It's pretty ridiculous. My guess, and it is a guess, is well over 500 to the wheels and whatever his weight is, plus fairly short gearing AIR. Same as my Vette though, I don't think it'd be particularly fast in teh 1/4 because the suspension is all wrong to launch worth a shit. It'd be like 12 @ 130 or something stupid like that.

[enkeivette]

Thanks? Haha.

Compression has always been this low. Even before the motor was first fired. I've often been cautioned by gear heads about it. But I have low compression, and fatty NA intended overlap. I really need a blower cam... and by B Day is 21 days away! ...just sayin :p

Engine makes power, doesn't burn oil, and the compression is consistent, it's fine.

[Shaolin Crane]

Thanks? Haha.

Compression has always been this low. Even before the motor was first fired. I've often been cautioned by gear heads about it. But I have low compression, and fatty NA intended overlap. I really need a blower cam... and by B Day is 21 days away! ...just sayin :p

Engine makes power, doesn't burn oil, and the compression is consistent, it's fine.

How did you test cranking compression before you fired it?

[94cobra69ss396]

What's your static compression, piston to head clearance and cam specs? The Chevelle has decent overlap with 246 duration at .050 and a 110 LSA.

[enkeivette]

How did you test cranking compression before you fired it?

Put the compression tool in the spark plug hole and ran the starter motor before I ever first fired it.

Compression is like 9:1, cam is 110 246 248? Or something...

[enkeivette]

Piston to head, don't remember. I think my pistons are like .02 down and the HG is .05. So prob .07. Some people cry about quench but the thicker HG/ lower CR was more important to me. AFR and speed talk tells me quench is of little consequence when the boost does the swirling.

[94cobra69ss396]

.070 isn't great but the Cobra is at .053 if I remember correctly. Even with the old 302 setup which had a compression ratio around 8.7-8.8 and a cam that had 110 LSA with 220 @ .050 it still cranked 150psi. Something isn't right. Does your car run good, sure. Could it run better, most likely.

[Shaolin Crane]

Put the compression tool in the spark plug hole and ran the starter motor before I ever first fired it.

Compression is like 9:1, cam is 110 246 248? Or something...

So before the engine was ever broken in? Not sure that would be an accurate compression test.

[enkeivette]

.070 isn't great but the Cobra is at .053 if I remember correctly. Even with the old 302 setup which had a compression ratio around 8.7-8.8 and a cam that had 110 LSA with 220 @ .050 it still cranked 150psi. Something isn't right. Does your car run good, sure. Could it run better, most likely.

Ive been through 4 HG replacements, probably 10 intake manifold replacements, and 2 sets of piston rings. What could possibly account for a uniform loss of compression in all cylinders, that does not cause oil consumption, loss of mpg, or at least a significant loss of power, while persisting through all of those changes?

Quench alone shouldn't change a compression reading. 9:1 with a 110 should produce the same measurement no matter how that air is swirling around in there.

Guy, yes, compression test was the same before and after break in.

[Shaolin Crane]

Ive been through 4 HG replacements, probably 10 intake manifold replacements, and 2 sets of piston rings. What could possibly account for a uniform loss of compression in all cylinders, that does not cause oil consumption, loss of mpg, or at least a significant loss of power, while persisting through all of those changes?

Quench alone shouldn't change a compression reading. 9:1 with a 110 should produce the same measurement no matter how that air is swirling around in there.

Guy, yes, compression test was the same before and after break in.

Ring gap, pushrod length, rockers, lifters, basically anything valve train related could cause uniform compression issues if something was not installed right or a wrong part was used. Not uncommon for people to think they have compression loss only to find out they have way too much preload on the valve train.

I don't have any one thing I can say it would be, however I do know that 9:1 should make a minimum of 130psi with a 110 lobe center. Are you positive you calculated the compression properly? What df the heads CC out to?

[enkeivette]

Ring gap changed to boost specs when I replaced all the moly rings with stainless. (Compression was the same with both rings sets).

Valves are adjusted pinky tight to zero lash, quarter turn of preload. Pushrod height and valve tip wear pattern checked when I installed the 1.65 harland sharp rockers. I did NOT over-tighten them, I am very aware of that mistake. (Compression was the same before and after different rockers).

Static compression, no, absolutely not sure. The history of this motor is that I relied on the machine shops calculation to yield 10.5+:1 compression, NA cam, dynoed it, down on power. Did the math myself after measuring piston depth with a feeler guage (pistons are relieved, heads are 74cc), calculated 9.4:1. Installed a blower, kept breaking pistons. Went with a thicker HG to drop it to a then calculated 9:1, saying bye bye to proper quench, and hello to functionality. (The closest I've been since the machine shop math blunder).

The end.

[Damian]

Reading through this whole thing a couple times, I think your problem is as simple as the carb itself. You said you cleaned it, but is it possible you put it back together not quite right?

[Shaolin Crane]

Ring gap changed to boost specs when I replaced all the moly rings with stainless. (Compression was the same with both rings sets).

Valves are adjusted pinky tight to zero lash, quarter turn of preload. Pushrod height and valve tip wear pattern checked when I installed the 1.65 harland sharp rockers. I did NOT over-tighten them, I am very aware of that mistake. (Compression was the same before and after different rockers).

Static compression, no, absolutely not sure. The history of this motor is that I relied on the machine shops calculation to yield 10.5+:1 compression, NA cam, dynoed it, down on power. Did the math myself after measuring piston depth with a feeler guage (pistons are relieved, heads are 74cc), calculated 9.4:1. Installed a blower, kept breaking pistons. Went with a thicker HG to drop it to a then calculated 9:1, saying bye bye to proper quench, and hello to functionality. (The closest I've been since the machine shop math blunder).

The end.

Which is exactly what I was getting at, advertised numbers are fun and all but they mean absolutely dick. AFR advertised my heads at 58cc and when actually measured, my first set were 65cc and the second set was 63cc. Same goes for the pistons with a 4cc relief that was actually 6cc. Piston depth is to be done with a dial indicator and degree wheel, blah blah.

So while 10.5:1, 9.4:1, 9:1 might be close, when you get precise you'll find out that it is probably closer to 8.6-8.8:1 which there is nothing wrong with, would explain why it runs better at that compression with the cam you currently have.

[enkeivette]

Guy,

8.6 would not surprise me at all. In fact it would explain the low compression gauge reading, and the tolerance of my 4032 pistons with that much boost ya? Plus, I gapped my rings on the conservative end for boost specs. What about my cam would be better off with low comp?

Damian,

Solved the problem. It was having severely oil fouled spark plugs on the left bank. Runs like a champ now.

[Shaolin Crane]

Guy,

8.6 would not surprise me at all. In fact it would explain the low compression gauge reading, and the tolerance of my 4032 pistons with that much boost ya? Plus, I gapped my rings on the conservative end for boost specs. What about my cam would be better off with low comp?

Damian,

Solved the problem. It was having severely oil fouled spark plugs on the left bank. Runs like a champ now.
MR. Vizard will explain it a ton better than I ever can
http://www.hotrod.com/how-to/engine/cam-lobe-centerline-angle-tech/

The dumbed down version is, your cam is meant to make good power N/A so cylinder pressures will reflect that, cycle compression will be higher, so add in boost, you either add octane, or pull timing and/or compression. Right now your compression, boost and engine is very much like a pro drag motor. They don't give much of a shit about "driveability" just "engine pressures".

[Shaolin Crane]

Here ya go, a good thread with discussion of Vizards cams
http://ls1tech.com/forums/forced-induction/1131757-discussion-about-turbo-cams-overlap-boost-reversion.html