see i've done alot of research on the h22 scince i have 2 of them in 2 diff. cars...they are different then the b18 becuase the walls are thinner lined and that they don't use the normal cross hatch design so when honing the pistons you have to use a special tool kinda clothy it makes a mirror finish... anyway the sleeves are there to strengthen the walls so that during higher boost level when the temp gets high and the thinner walls start to flex(or whatever you want to call it) its stable and reinforced so you don't eject a piston through or out of your motor...