[AcesHigh]

Yes, it is a combination of the three. The H22A head flows noticeably better than the H23A, resulting from variable valve timing and head design. If you notice, torque between H22A and H23A are roughly identical; VTEC just lets H22A safely produce power a little bit longer than H23A. Essentially, more displacement does not necessarily equate to more power as long as the cylinder head itself is the limiting factor. This is why some people were contemplating putting the more efficient H22A head on the H23A block. With the H23A alone, the larger displacement gives you more low end torque, but the torque curve will fall faster on it versus on the higher revving H22 and power will be the same. Without the head, H22A and H23A are roughly equals.