[screamingchief]

Originally Posted by leeklm

Sorry to hijack the thread, but this topic is timely... My new forged SRP piston instructions call for a minimum of .0025/.0030 wall clearance for a 4.2" bore (see attached). My local engine guy made the bore 4.185, which gives us about .0035 clearance.

Based on the instructions, i assume this will be fine for an aluminum head 455 street engine?

Originally Posted by Tom Vaught

It depends somewhat on what the piston material is.

SRP pistons are 4032 vs. most dedicated "race" forgings being 2618.

The two materials have differing expansion rates thus different P2W specs.

The pistons these guys are talking about are all 2618 I'm sure.

And usage also comes into play,high CR,boost,nitrous all can require more P2W as SOP due to the additional heat the pistons "sees".

My first thought when I saw the "What is a ideal piston to wall clearance on a N/A motor?" was .005" to .007" as a good "middle of the road" number for the bulk of applications,but then again I prefer the 2618 pistons as SOP as well,but yeah the 4032 pistons (and whatever material TRW/FM forgings are made of) can indeed run closer than that in many applications as well,they just are'nt as strong as a 2618 piston would be.

HTH

Bret P.