GM performance ZZZ engine piston replacement

The ZZZ uses a cast piston, if it has slap, something is seriously wrong. Your going to have to open it up and take a look at the cylinder walls before doing anything, if any one of these cast pistons is busted the block will require a rebore and that will establish the replacement piston size. There are lots of excellent pistons out there for 350’s. A hypereutectic casting would be stock replacement material, 2618 forging is racer stuff very strong but needs a wider clearance and warm up time to quiet the skirt to wall slap. Forged 4032 is a very good street, part time racer piston it’s high silicon alloy is thermally stable so this allows more factory like clearances, therefore, it runs quieter throughout the engine’s operating temp range.

My preferences run to floating pins which dictate a much needed rod change for this engine. The crown should be either D dish with a tight 64cc chamber head or a flat top with a 72-76cc chamber head. The ZZZ came with L98 head’s while not the worst head Chevy ever produced they are technically obsolete as of the LT1 and 4 mid 90’s head that don’t fit the Gen-I block cooling system, next much better factory head is the iron L31 head of 1996 up. The factory sells the Fast Burn head which is a chamber and port copy of the LT1/4 head for conventional cooling blocks. The aftermarket has a plethora of excellent to fantastic head’s for the Gen-I SBC in various chamber volumes in either aluminum or iron.

The L31, Fast Burn, the aftermarket as well as the reverse cooling LT1/4 head’s all use the Ricardo high swirl, central plug chamber. As far as the aftermarket goes these are usually available in 62-66cc chambers or 72-76cc chambers. In the latter large chamber these are not the open chamber typical of GM SMOG head’s, the aftermarket uses a Ricardo configuration that is just a bigger volume than the small chamber versions. If you modernize the L98 64-66cc chamber head’s you have then these aftermarket head’s let you play with piston crown configurations to dial in the compression you need to have.

The ZZZ sets the piston .025 inch in the bore and uses a .053 thick head gasket, this is not efficient with aluminum head’s. Aluminum head’s really need the block decked or raised crown pistons to use the thicker composition head gasket to get the squish/quench clearance toward the idealish .040 inch dimension. Here you have to look at avaibility of parts to dial the squish/quench clearance in to as close to the magic number as possible.

Bogie