I had bought some srp pistons for my LS bottom end a while back which the seller claimed to be standard bore size. When I went to install them, it wouldn't go into the block, and my friend told me that it was an oversize piston because it had the number 20 (.20 oversized) on the bottom of it. So then I sent the block to get it bored out for the pistons and now I have piston slap cold and warm engine(less when warm).

Anyways, today a I saw another set of SRP pistons for an ls that is claimed to be standard size and it had 20 on the bottom of it too. So does that mean the 20 has nothing to do with the size, and I was just a dumbass and overbored my block?

 

SRP has pistons in std.,+.010,and+.020.Any real shop would measure the pistons,not go by any stamped numbers.Forged pistons are going to make a little more engine noise than the cast stockers.A std. piston in a plus twenty bore would smoke and break the skirts in no time.Ask the shop if they remember what they used for piston to wall clearance and check with SRP for the recomended numbers.
Glenn