Compression Test
Thread Starter
Advanced
Joined: Jan 2000
Posts: 67
Likes: 0
From: Wood River IL
Compression Test
What PSI should I see doing a compression test on a LT5? I glanced through the service manual and didn’t see a spec for this. Forgive me if it is there and I missed it.
Thanks,
Uncle Robin
Thanks,
Uncle Robin
Safety Car
Joined: Apr 2000
Posts: 4,644
Likes: 4
From: Texas, GOOD OLE USA
Re: Compression Test (UncleRobin)
If it twists the needle off the gauge as it goes around then you have just enough. My race engines run in the 240 to 280 range but not sure about an LT5. I'll be watching this one to get schooled :seeya
Safety Car
Joined: Dec 2000
Posts: 3,712
Likes: 16
From: Town of the cow
Re: Compression Test (UncleRobin)
Consistancy is more important than the absolute pressure value (within a given range). I have heard that GM would not perform compression tests or was that leak down checks on the LT5 because they were getting inconsistant readings? This doesn't make sense but had heard it somewhere.
Thread Starter
Advanced
Joined: Jan 2000
Posts: 67
Likes: 0
From: Wood River IL
Re: Compression Test (UncleRobin)
OK here is what I have got, a LT5 with 40k on it that came out of a wrecked ZR-1. The engine had been sitting for 3 years. I pre-lubed the engine before starting to turn it over, as I figured the bearings would be dry from sitting for so long. The first compression test netted these results:
1 - 250; 2 - 245
3 - 150; 4 - 250
5 - 250; 6 - 230
7 - 180; 8 - 210
Then I put a little oil in each cylinder. Then I got these results:
1 - 270; 2 - 270
3 - 270; 4 - 260
5 - 280; 6 - 260
7 - 270; 8 - 270
One good thing, it looks like the valves are OK. My guess the rings are not seated/sealing from sitting so long. The question is, is it temporary and the rings will be ok after it turns over awhile? I am going to let it sit overnight and see what the compression test yields tomorrow.
Anybody care to offer some feedback on the compression test results?
Thanks,
Uncle Robin
[Modified by UncleRobin, 8:02 PM 8/19/2002]
[Modified by UncleRobin, 8:02 PM 8/19/2002]
1 - 250; 2 - 245
3 - 150; 4 - 250
5 - 250; 6 - 230
7 - 180; 8 - 210
Then I put a little oil in each cylinder. Then I got these results:
1 - 270; 2 - 270
3 - 270; 4 - 260
5 - 280; 6 - 260
7 - 270; 8 - 270
One good thing, it looks like the valves are OK. My guess the rings are not seated/sealing from sitting so long. The question is, is it temporary and the rings will be ok after it turns over awhile? I am going to let it sit overnight and see what the compression test yields tomorrow.
Anybody care to offer some feedback on the compression test results?
Thanks,
Uncle Robin
[Modified by UncleRobin, 8:02 PM 8/19/2002]
[Modified by UncleRobin, 8:02 PM 8/19/2002]
Safety Car
Joined: Dec 2000
Posts: 3,712
Likes: 16
From: Town of the cow
Re: Compression Test (UncleRobin)
Was this test done cold? If so, that would increase the amount of leakage you are getting through the rings. Proper compression tests should be done at operating temperature.
Safety Car
Joined: Apr 2000
Posts: 4,644
Likes: 4
From: Texas, GOOD OLE USA
Re: Compression Test (4cefed)
Was this test done cold? If so, that would increase the amount of leakage you are getting through the rings. Proper compression tests should be done at operating temperature.
The numbers "seem" healthy. :seeya
Thread Starter
Advanced
Joined: Jan 2000
Posts: 67
Likes: 0
From: Wood River IL
Re: Compression Test (UncleRobin)
It looks like good news. After letting it sit overnight, I just did a compression check and got good consistent numbers.
1 - 265; 2 - 260
3 - 260; 4 - 255
5 - 270; 6 - 255
7 - 260; 8 - 260
The engine is out of the car sitting on a stand. Before I put it in, I wanted to make sure the engine was OK. It was a used engine which turned out to be “more used” than I expected when I bought it. It looks like I won’t have to pull the heads. :D
Thanks for the help.
Uncle Robin
1 - 265; 2 - 260
3 - 260; 4 - 255
5 - 270; 6 - 255
7 - 260; 8 - 260
The engine is out of the car sitting on a stand. Before I put it in, I wanted to make sure the engine was OK. It was a used engine which turned out to be “more used” than I expected when I bought it. It looks like I won’t have to pull the heads. :D
Thanks for the help.
Uncle Robin
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
