hey im looking for pistons for my turbo set up ( i thought it fit better under tech, than fi) and i was wondering what size i would need. i have a b18a and the options for that are 81mm 81.25 & 81.5

 

I would go standard 81mm-- if you happen to scar up the cylinder walls, it gives you more leeway to reuse your block. If you were to use 81.5mm, and you scar up that cylinder wall by a dropped valve or bad ring lands, you'll need a new block.

 

take the block to the machine shop first, then buy pistons. if your cylinders need to be bored because of severe out of round, taper or scoring you will have bought pistons that wont fit.