so the 315 and the 920 have identical port sizes. Probably the same head with a different bolt angle, Im wondering if the data was on 2 different test benches.
And both are listed as having the same closed combustion chamber. 57-64.5 cc's. The #675 head (3 different part numbers) were open chambered and had chamber cc's between 60 and 67/5 cc according to the Larry Shepard book.
