Engine experts please come in!
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
PCV is goods as far as I know. Took one of of another LT1 with no change in engine performance. Builder took intake off and resealed because plugs were fouled and continued to be wet until I changed the exhaust manifolds to Hooker headers. But still still have an almost constant flow of smoke out the exhaust.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by 66grandsport
Builder says he loves the Total seal rings and loves the 230 compression. Says he has put many sets on.
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Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by CFI-EFI
Even more reason to cast a doubt on the builder. That cranking compression of 230 psi is a definite tip off to a problem. It is more than likely with the camshaft and it's installation.
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Racer
Joined: Feb 2006
Posts: 269
Likes: 0
From: Vancouver B.C.
Originally Posted by bogus
that it wasn't degreed properly?
66Grand,
It's not that you have too much compression.......it's that you have it at the wrong time. Your cam overlap should have reduced the compression down significantly.
Cruising
Joined: Jul 2006
Posts: 11
Likes: 0
From: Victoria BC
Originally Posted by edcmat-l1
I have seen oil control problems that couldnt be verified with a leakdown test. I think the extra oil around the top 2 rings interferes with the test. Now if it had a groove wore in the cyl wall from a broke ring, that would surely show up. Also, Ive seen oil ring problems that cause oil control issues, and a leakdown will never tell you anything about an oil ring. The dead ringer is if its got a bunch of blow-by. If not I would be looking elsewhere for the oil prob.
I'm not familiar with the LT4 hot cam as I've never used one, but I too am suspicious of the compression numbers. It doesn't explain the excessive oil consumption, though.
That being said, I'm also suspicious of having soft rings considering the amount of compression it's building - assuming the compression numbers are consistent across the board. Perhaps a valve seal(s) got shredded during assembly?
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Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by 66grandsport
How do I or would I know if it is blow by?
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by CFI-EFI
Even more reason to cast a doubt on the builder. That cranking compression of 230 psi is a definite tip off to a problem. It is more than likely with the camshaft and it's installation.
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Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Even if the rings weren't seated? a quart of oil every 300 miles is sure going somewhere! I'd like to watch him do his compression test. I'm kinda wondering if he hasn't got a broken ring in there?
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by rick lambert
Even if the rings weren't seated? a quart of oil every 300 miles is sure going somewhere! I'd like to watch him do his compression test. I'm kinda wondering if he hasn't got a broken ring in there?
Broken ring
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by edcmat-l1
383,SRP forged pistons, probably flat top single eyebrow, lt4 cam. I dont think 230 is out of the question.
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Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
I've seen 9:1 motors with baby cams have 230 psi cranking. I've also seen 12.5:1 motors with racing cams have 175 psi cranking. We dont place too much value in the actual #s, more in that they're all the same. For diagnostic purposes its more about HOW it makes compression, usually first pulse amount. Leak down testing is also very valuable info, but not really pertinent (typo?) here. I think we're on the wrong path here. I'd definately like to see some scan data. Whats the fuel trim #s? if it pings on 100 octane, its got serious problems. I could see the quench area being an issue, but its definately not too much comp.
Melting Slicks
Joined: Jul 2006
Posts: 3,356
Likes: 1
From: Chesapeake Va
Originally Posted by CFI-EFI
The compression ratio only has a minor effect on the cranking pressures. It is the cam timing that has the greater effect. That has nothing to do with the oil consumption, however.
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