The F22 runs 85mm pistons, the reason that raceeng.com has 85.5mm pistons is because when they ordered sleeve kits from darton, darton machined the sleeves to be 85.5mm bore, therefore making them useless with the standard pistons. I know this for a fact, because I was the person who ordered the first sleeve kit from raceeng.com that was machined to 85.5mm and I had to return my original pistons and wait for wiseco to make the 85.5mm ones.