ok with the frm bore on the h22 i understand taht forged pistons will not work due to the frm.. i know that mahle gold series will work but longevity is sacrificed.. now they say only oe pistons will work.. now is that because the oe pistons are cast or are they made with a special material... and is there a difference in the rings??? if i bought cast pistons that were a type s knockoff will they be compatible with the frm bore??