short of tearing my new engine apart, how can i find out my comp ratio?i bought this 496 short block and the # on the reciept is not what i have for pistons. the #on rec is 142978 which is a flat top piston with a relief in it. i remember seeing a small dome on the pistons before i bolted new afr 315 heads on it.if i do a compression test is there any way to figure that out? or do i need to pull it apart again.? reason i need to know is i might be putting a procharger on it, so i need to know what i have.

Maybe you could find someone that has one of thoses fiberoptic tools that you can insert into the cyl through the spark plug hole that lets you see inside the bore. Then you can get the #'s off the piston if motor hasnt been run yet and doesn't have carbon on the pistons yet,you can see that tool in EASTWOOD TOOLS.

Heck,you really dont have to see the pt# on the piston,you just need to see if there is a dome or not and then you will know what you have.

I would thinkg a static comp check would give some kind of indication of comp ratio weather it be pretty hi or pretty low but nothing inbetween but thats not an accurate way to approach it esp when cam choice will have a big factor in static comp test results.

i would think if you truely remember seeing domes on the pistons then that's what you have and the pt# on the invoice is a mistake.

Scott

A compression test will not help you determine static comp. If you tested 2 different duration cams, the readings would differ, due to the amount of pressure they bleed off.

It's easy to tell a big dome from a small dome. That appears to be an SRP part number but isn't close to what a 496 would have(4.530 bore). The most popular sizes for a 496 are 5cc(about 9:1, closed chamber design), 18cc(about 10:1) and 43cc(about 13:1). You should be able to tell by looking. If it had a really small dome it could be one of the last two here. Do these look familiar?
http://www.jepistons.com/cat/srp/auto/chevy_bb/small_dome_closed.shtml