A real bad assumption has just been floated. 906 heads are NOT 88cc, some are, but they can be found anywhere from 88 (or lower) to 92 or so. Not that 2cc makes much if any difference on a 400 size cylinder.

If you were to get all the longtime engine builders on this board to recall every 906 head they ever cc'd I bet you would hear at least one "94".

A 915 should measure about 84cc.

Your mileage may vary!

R.