Originally posted by "speed_daemon1"
The actual combustion chamber in the b16 head is larger than the b18c by a couple cc's.
However the b16 head is supposed to flow the same as an ITR head, so it's a trade off of flow characteristics for compression. You can always shave the head or run a thinner head gasket to bring it back up.
Not too sure on a b18c head on a b16 block, haven't really heard of anyone doing that. Not saying it hasn't been done, just that I don't know anyone that's done it.
the ITR head flows a bit better than the B16A head (due to factory port & polish, different cams, etc).. BUT.. the B16A head flows better than the GS-R head.
the ITR head happens to be cast from the same casting as the B16A head, so a little bit of port & polish work, and an ITR/CTR valvetrain, and a B16A head will flow as well as a B18C5 or B16B head.
compression ratio isnt JUST determined by combustion chamber cc's tho. engine stroke is a factor as well.
CR = (cc vol + cylinder displacement) / cc vol
the same head will have a higher compression ratio on a B18 block over a B16 block because of the added stroke (assuming you use the same pistons in both blocks, because piston dome/dish shape affects cc volume).