Has anyone run the 85.5mm Supertec pistons with boost? I was wondering if the walls become to thin at that point.

 

Why couldn't you bore then sleeve the block?

 

Good idea.

 

Sonic test block. Close attention to top of bore on thrust side. .090 absolute minimum, .120 preferred.

 

This. We threw a perfectly good 01 block away this year because an incompetent engine shop decided to jam 85.5s in it without checking first. #3 came out at .060" and the customer was forced to supply us with a new block to continue the build.

 

It sounds like the 84mm are the safe bet then. Are there some years that have more material than others or is it just luck?

 

That block averaged .060" thick on the front side of the bores... the thinnest spot was .049"! The thin area was also about .400" tall just under the deck, which is the worst possible place for it to be thin. Having only sonic checked that one block, I don't know if the block castings are subject to core shift, or whether the machine shop machined it incorrectly as the rear of the cylinder walls averaged ~.200".

If you really want to throw a big oversize in, I'll second Emilio and say definitely sonic check it. I'd also tend to stay towards the thicker side of Emilio's recommendation for any FI engine.