Big Block Chevy Compression Weirdness

GEOMYCYK

MEMBER
CHEVROLET

Hello,
Recently purchased a 1980 Suburban with a transplanted 454. Engine was bored 30 over and got a new cam and oval port heads by the previous owner. I did a compression test on all of the cylinders this afternoon and this is what I came up with. All 4 of the cylinders on the driver's side were right around 10 to 1, while all of the cylinders on the passenger side were right around 11 to 1. Any ideas on what may be causing this difference in compression from one side ot the engine to the other? All engine work was done before I purchased it and I have no idea if the work was done by a qualified mechanic.

Any and all help is greatly appreciated.

1 Reply

BURRBRIAN

MECHANIC
158 POSTS

Hi, It kinda sounds to me like you might have different thickness of gaskets from one side to the other. Or if the heads were re-worked and had any shaved off the chamber side one got shaved more than the other. Or possibly the pistons on one side were farther in the hole than the other. To find out for sure there is going to have to be some measuring done. Meaning if you are to find out what has happened the heads need to come back off and the chambers on the head measured and the deck hieght measured-how far the piston sets in the cylinder at TDC. To get things evened out the block deck may need to be shaved or the heads do. And make sure the gaskets match if you have this done. Pretty much machine shop work unless you are really into motor building and have a lot of special tools. Not sure how you came up with your figures though, comp. Tests show how many lbs.-Sq. In. Of pressure in cylinder while you are giving a ratio as to area compressed on the piston stroke. Whichever, you have to look at the things mentioned to find out why you have the differences. Good luck.