I have a B16A with a GSR head, the GSR head has smaller volume, i think its roughly 41.5cc, while the B16A has like 43cc... so I get a compression ratio of about 10.6-10.7... which is roughly .5 points higher, and you can feel a small increase in torque all-throughout the powerband, and a small increase in HP... It's an easy 10HP for every compression point u raise it, so that must be true... for me i had a skunk2 IM but the bolt patterns are different for a B16A and a GSR head... so I had to use GSR IM, but u can still tell a difference. I changed them B/C 3 days B4 we were goin to change the timing belt, it broke... so I thought valves were bent...Also, COLD AIR INTAKES suck ass if u don't have a Patented breather valve, cause I had one till it sucked up a gallon of water and bent the number one cylinder connecting rod like a a banana,LOL.