wondering if anybody knows what wrong with putting forged pistons in stock h22 block without resleeving it?

 

the h22 frm (friction reducing material) in the cylinder walls you can't run forged pistons because the two materials used are not compatible.

 

mahle

 

frm does not mean "friction reducing material"
it means Fiber Reinforced Metal.
The fibers is a carbon based fiber and the metal is aluminum. It allows the metal to be very strong, but htin. the problem is that the sleeves are not forged, and forged aluminum is hardner than FRM, so it galls and then tears the sleeves up, unless the piston is designed for the h22 sleeves.