Small block compression

[Orionsax7]

I finally got around to doing a compression test on my 318 w/ 360 J heads. Don't know if the heads were milled because this was done before I got the engine. I got 110 to 115 on every cylinder. What does this work out to? Is there a compression chart or something I can follow?

-Alex

 

[Mrmopartech]

A normal compression of 150-170 is whats needed.You either have a smog motor with no cam,or a motor on its way out.What,s even a better test, is a leak down test to determine what is leaking.has your motor ever been opened or rebuilt?,and what was done to it?You could have badly seating rings or ones that are toast,or valve seats that are done.One other that can cause this is a badly installed cam,not degreed right,causing low compression.Mrmopartech

 

[Orionsax7]

The block appears to be a 78 318 w/ 71 360 j heads. I don't know how the cam was installed because it was already in there when I got the motor. I had the heads rebuilt about a year and a half ago. That was the last time it was opened. The short block was not rebuilt. I did notice that it was already .030 over and had a step in the walls. I didn't want to have it rebuilt, for me it wasn't worth it. I'm building a nice 360 for it. Just want to know what might be going on tin this engine.

-Alex

 

[dgc333]

A 78 is a low compression engine and the 360 heads have much larger chambers that lower the compression even further (unless of course they were extensively machined).

The numbers you have can be expected.

 

[moper]

Thats right for the big chambers, and stock style pistons in it..there is no direct comparison with static ratio, and cranking pressure. But, you know it's low.