Practically all engines are optimized for part throttle efficiency, since they live 99% of their time between idle and 20-40hp.E.Roy wrote: ↑Tue Jan 14, 2020 7:28 pmYou touched on something I feel to be true with my limited experience, and that is the pushrod bump can screw up the column of air and cause the flow to detach from the short side. On an uported 906/062 Vortec iron head, I feel Chevy engineers put deliberate shapes at the pushrod pinch to force air to flow down the straight side for part throttle velocity. I feel the whole port is optimized for part throttle efficiency and swirl, which makes sense given 906/062 were on a truck motor intended for 4-speed auto potentially towing 8,000 lbs at 2,000rpmmag2555 wrote: ↑Tue Jan 14, 2020 6:30 am With a 23 degree SBC head in terms of aftermarket ones you need to to be in port volume range of 195 to 215 CCs and air flow numbers of greater then 270 cfm@28" before the port area at the push rod buldge becomes a choke point, and even then the flow loss seen is more due to the air stream being forced to compress and then realign itself once passed that pinch point.
Oddly a truck engine should be better at higher loads compared to, say, a passenger car that only needs 20hp to tool down the road at 60mph.