My sissel kirby lump port flowed the most of any head I have used. My stock siamesed head w/ dividers flowed 25% less than the lump port head My GM 12 port from Brazil flowed the same as the stock head w/ dividers.
I am not a head specialist, and I agree that the lump port improves the short side radius for increased air flow, but I also think the deduction of port size increases air speed and helps fuel mixture.
On a chevy 6 the port choke area is at the port opening like a small block chevy is at the pushrod area. The choke area determines at what RPM your port will become choked because the air speed goes to mach and VE drops real quick. If you keep the RPM below this number you will not have any problems.
I designed my intake to be an extension of the port so it mimics a small block chevy in that the port opening is large and tapers smaller then expands to the valve pocket, unfortunately it will not fit on the flow bench with the intake and exhaust as one part.
Since I run a turbo they like high gearing and I don't need to run a lot of RPM and can get by with a small port area.
