57 cc?
I don't agree with that information because my 1st hand proves that wrong. Most books are out there with some of the crap printed as fact. Ever see any factory x heads at 64cc? That's the kinda stuff that gets printed.. lol
Just the visual gives it away that the 302 is smaller than the 920 by the 920's lack of the peak/point on the closed part of the chamber. My 302's pulled from off a bone stock 318 were wire wheel cleaned measured 64cc. I checked 315 and they were 66-66.5cc
The 920 heads I have currently had hard seats and a valve job. So while you could say they grew... the exh seat got higher by being replaced and the offset is nil. I measure them later today around noon.