is there any way to tell the compression on my 396 when i know zip about whats in it, but its surpose to run good we shall see in the spring .

 

No you can't with the engine still together. To calculate c.r. you need to know what type of pistons (dished, flat top, or domed), the c.c. chamber size of the heads (which you can find out by looking up the casting numbers), whether or not the heads have been shaved, compressed head gasket thickness and bore diameter, and whether or not the block has been decked. There's no way of knowing all that without taking the top end of the engine apart and doing some measurements.

 

thanks for confirming my thoughts

 

You can get an idea by doing a compression test. Not going to tell you that it is exactly 12.2:1 but will get you in a ballpark. I have a 555 13.2:1 big block that produces a compression test number of 230 psi per cylinder. My 468 big block is 10:1 and a compression test produces a number of 180-190 psi. Then I have a 350 that is 9:1 that compression test produces a number of 150-160 psi. So basically the higher the psi the higher the CR. But if you want an exact number you will have to tear it down and measure the combustion chamber, determine what size dome or dish in the piston and figure in what size head gasket you are using to get the exact number.