piston wall clearance for 10-15 pounds of boost.
 

im dropping a couple 400s off next week for some machine work, 1 of them i plan to throw some slightly used parts in and slap a blower on. the pistons are ross .030 pistons that normally would need .004-.005 pwc. right now they measure 4.145 -4.146 on the skirts. if i were to have the cylinders honed to 4.151, or even 4.152 would that hurt? or would it even be neccessary to go after that extra .001-.002 clearance?

Wouldn't hurt at all if you got the skirts coated. https://www.line2linecoatings.com/

Coupled of questions: Are you going to have it honed with a torque plate? If no, then IMO you need the extra clearance to keep from scuffing the skirts when the cylinders get all out of shape when hot and under boost. If honing with plates, an honest .006" piston to wall is enough at the tightest spot. Check your Ross box or instructions for the "gauge point" they want you to use for your skirt measurements. Every piston manufacturer seems to have a preferred spot. It's often not at the very tip of the skirt. Good luck with your build.

iam going to have it honed with torque plate. ill have to see if its still in the box they came in. i was measuring about mid way up the skirt but i probably should double check

I am at .006 piston to wall with Ross pistons on a NA build. (filled block)
And you can not hear the pistons making noise at all.
So I would run that .006 in a boosted engine in a heartbeat.
Its better than scuffing.

i ended up using the ross pistons on a na 406, and bought some icon forged pistons to use with my 4.0 crank and blower. Iam having the cylinders final honed to ..006 p w clearence