Probably been covered before, Will s2 heads Fit on a s1 bottom end with the s2 lower plenum? Or another way of putting it, did the block change at all between s1 and s2?
Another difference with heads are 89-94 are stamped 40P, whilst the 95+ are stamped 48P which I'm told have bigger ports
Doesnt really have bigger ports, its more the fact that you cant port them more without hitting a water gallery. S1 heads get paper thin when doing serious porting... Im still trying to find the cross section picture..