I bought a complete top end kit from Koffels several years back, I had them port them, there flow sheets said 420 CFM at .600 lift, 430 at .700 and above to .900 and no stalling. I haven't used them yet so no other input besides that. I have had Jeff at MCH do three different types of heads on his CNC programs, two sets of 440-1, one set of B1-BS and one set of Eddy RPMs, all of those motors made really good power on the dyno and in the car Big air, big power