I've been reading up on pistons lately and do you have to bore over your block for them to fit? or is that just an optional choice to boost HP, the reason I am confused is cause when looking at Pistons it gives a bore size so it is throwing me off.
if the walls are scored and warped you have to bore the walls out to straighten them and get a good ring seal. then you choose the piston that has the same bore as the cylinder's new bore.
if the walls are straight and not scored to prevent a good ring seal, you don't have to bore and you choose the stock piston bore size.
you won't know until you have the walls looked at after the block is removed and the old pistons taken out. some people don't want to wait to see (downtime longer) and just order the piston with the bigger bore ahead of time and so they just go ahead and bore anyway. that way they know that their walls are straight guaranteed. if you exceed 81.5-82.0 mm, you need to resleeve.