i am looking to buy a built zo6 block with standard ls1 stage three port done. their are forged dimand piston in the block but the owner has no idea what the compression is. i am assuming the shop where he paid for the build just ordered standard compresion pistions. so with the heads what compression whould that be? thank you in advance.

 

it will depend on if your heads have been shaved any. also the diamonds will have either an -2 or -4 cc valve reliefs in them probably so compression will be lower than stock if heads are not milled down any.