LSX 376 Compression Test Numbers ok?
Thread Starter
Launching!
Joined: Feb 2012
Posts: 263
Likes: 50
From: IL, USA
LSX 376 Compression Test Numbers ok? Motor is a Supercharged LSX 376 (9:1 CR) - I had some fueling issues and the motor leaned out and broke some of the spark plug porcelain and tips. I let off the gas right after I heard the pinging etc. Used a borescope and did not see anything in the cylinders except some small markings on the top of some pistons (I assume from the pieces of spark plug). Now I also hear a sort of slight tapping coming from the heads (sounds like driver side head mostly) sometimes the tapping is slight and sometimes a little more louder but not very loud...
Did a compression test and this is what I got (cold engine, no spark, no fuel and WOT - cranked over for about 8 seconds each) :
Driver Side : 1 - 150psi, 3 - 146psi, 5 - 140psi, 7 - 124psi
Pass Side : 2 - 150psi, 4 - 148psi, 6 - 140psi, 8 - 148psi
Idk, what do you guys think? I am gonna pull the heads out as Im wondering if some of the pieces damaged the valve, valve seating etc...
Did a compression test and this is what I got (cold engine, no spark, no fuel and WOT - cranked over for about 8 seconds each) :
Driver Side : 1 - 150psi, 3 - 146psi, 5 - 140psi, 7 - 124psi
Pass Side : 2 - 150psi, 4 - 148psi, 6 - 140psi, 8 - 148psi
Idk, what do you guys think? I am gonna pull the heads out as Im wondering if some of the pieces damaged the valve, valve seating etc...
Thread Starter
Launching!
Joined: Feb 2012
Posts: 263
Likes: 50
From: IL, USA
Usually bad valve stuff results in zero compression, not low compression. Put a spoonful of oil into #7 and retest, see if the test improves. If so, it's a ring issue. cyl 7 on these things is known for going lean due to the way air flows in the intake. 7 just gets more air
TECH Senior Member
Joined: Jun 2016
Posts: 22,298
Likes: 3,619
From: Central Cal.
Usually bad valve stuff results in zero compression, not low compression. Put a spoonful of oil into #7 and retest, see if the test improves. If so, it's a ring issue. Cyl 7 on these things is known for going lean due to the way air flows in the intake. 7 just gets more air
Just a bit of mental rambling.....
Yeah its usually due to poor valve seal or the rings themselves but he was bleeding off pressure around the spark plug hole on the tool and once he got that straightened out he was finding 140+psi on No. 7.
