The 3.4 block is a totally new casting, designed with the larger bores in mind. So, even if you overbored a 3.4 .040" (or whatever arbitrary overisize), the cylinder walls would be no thinner than a 2.8 bored out .040".

I used Sealed Power pistons for my 'Stroker' project. You can get them with teflon-coated skirts. The teflon coating allows for very tight piston-to-bore clearances, eliminating the dreaded GM 3.1 piston slap and skirt wear issues.

I can testify that with cyl's bored to the tight end of the mfr's specs, the pistons were a snug fit indeed. But the motor is real tight and doesn't burn a drop of oil.

Part # for the pistons I used: Sealed Power H562CP .75MM; the "CP" in the part # stands for "Coated Piston".

I have a nice set of 1.00MM (.040") pistons, same brand, that I snagged off eBay Dirt Cheap. These are awaiting a Project-to-be-Named! That one will see the performance cam and other goodies and should be very Sweet. <img src="/forums/images/graemlins/cheers.gif" alt="" />