Seems like oem's performance, gets most of our attention. Many times, it's for good reasons, like bang per $. Case in point, the new "Apache" 6.4L hemi head. Stone stock it's rated int. flow is 340-352 cfm. @ .6" lift,( 2.155" dia. helps) A new, complete head sells for $450.+ $150 core charge,(yeah, it must be the new math). Boosted/built 6.4's are reportedly sustaining 1,300 rwhp.Did I mention, this is a "small block" ? Comparing to the smog choked dark days of 75', it appears the Big Three hp. wars, have recovered well. Faster-safer, roverman.
Impressive numbers Art, probably has Chevy and Ford looking over their shoulders :)
No big mystery about these, the valves are inclined 18 and 15 deg., away from bores. With a 2.155 int. and a 1.65 exh. and virtually zero shrouding, it's easier to go-with-the- flow. roverman.