Compression test numbers for 9:1 ok?
Thread Starter
Pro
Joined: Apr 2014
Posts: 722
Likes: 55
From: IL
Compression test numbers for 9:1 ok?
I did a compression test on my lsx376 (like a iron block forged ls3 basically), which has 9.0:1 compression and got around 140 - 155 across the board. Is this ok?
Drifting
Joined: Mar 2018
Posts: 1,365
Likes: 414
From: New Jersey
I would say it's ok. Since the readings are pretty even. Was the engine warm or cold? How did you do the test? Big cam?
Safety Car
Joined: Jul 2010
Posts: 3,973
Likes: 386
From: Chandler AZ
Someone on a truck forum had some calculator that gives compression psi range expected with compression ratios, only thing was different camshafts could alter the numbers.
Le Mans Master
Joined: Jul 2010
Posts: 6,008
Likes: 723
Race Director
Joined: Oct 2004
Posts: 12,864
Likes: 4,666
Last edited by grinder11; Jun 9, 2021 at 06:14 PM.
Safety Car
Joined: Mar 2017
Posts: 3,768
Likes: 940
From: Orlando Florida
140 is low. All plugs out, battery fully charged, and throttle fully open?
I'd like to suggest that the follow up is a cylinder leak down test. The two together will really tell you where you are.
I'd like to suggest that the follow up is a cylinder leak down test. The two together will really tell you where you are.
Thread Starter
Pro
Joined: Apr 2014
Posts: 722
Likes: 55
From: IL
Last edited by vettefx76; Jun 13, 2021 at 02:56 AM.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
heard the throttle wide open thing too I dont see how that affects anything .The cyl will get the air it needs either way.
150-60 for a low comp engine is just fine nothing to worry about. If you really want to know its health do a leakdown test.
150-60 for a low comp engine is just fine nothing to worry about. If you really want to know its health do a leakdown test.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
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
Safety Car
Joined: Aug 2011
Posts: 4,447
Likes: 409
From: Portland OR
Why are you checking it?
Warm engine. All the plugs out.
and yes, you need that Oring
Its 9:1, cam has some overlap. Those numbers sound fine to me. Spread is a little high, but w/o that Pringle’s to seal the tool to the plug hole, all bets are off.
Holding the throttle open helps.
Disconnect the injectors.
Id do it again
Warm engine. All the plugs out.
and yes, you need that Oring
Its 9:1, cam has some overlap. Those numbers sound fine to me. Spread is a little high, but w/o that Pringle’s to seal the tool to the plug hole, all bets are off.
Holding the throttle open helps.
Disconnect the injectors.
Id do it again
Thread Starter
Pro
Joined: Apr 2014
Posts: 722
Likes: 55
From: IL
Why are you checking it?
Warm engine. All the plugs out.
and yes, you need that Oring
Its 9:1, cam has some overlap. Those numbers sound fine to me. Spread is a little high, but w/o that Pringle’s to seal the tool to the plug hole, all bets are off.
Holding the throttle open helps.
Disconnect the injectors.
Id do it again
Warm engine. All the plugs out.
and yes, you need that Oring
Its 9:1, cam has some overlap. Those numbers sound fine to me. Spread is a little high, but w/o that Pringle’s to seal the tool to the plug hole, all bets are off.
Holding the throttle open helps.
Disconnect the injectors.
Id do it again
I checked the cylinder bores with a borescope and did not find any damage just what appears to be some detonation marks. I was told the pieces either disintegrated from the heat / managed to go out thru the exhaust. Thats why I did the compression test. I really want to pull the heads and check although the car is running like it was again except I can hear a very slight tapping sound from the heads....
Last edited by vettefx76; Jun 14, 2021 at 05:05 PM.