both heads are ALMOST the same because the compression height of the piston in inches are the same(1.154 in.), the cylinder head volumes are the same,(32.8cc's), and the valve sizes are the same too(30/26). i think the only differences are the Y8's intake manifold and cam profile. lift, grind, duration ect. SO the heads are TECHNICALLY the same, I say get the Y8 for that 2 extra horses!!!