Larry on his approach:
Now I'll address your head related questions: With the exception of blown applications, ports don't just flow one direction. Intake ports pulsate back and forth, and exhausts flow backwards too. This occors primarily at overlap, when the cylinder still has positive exhaust trying to exit the exhaust port ...where header back pressure is pushing backwards. Now the intake valve (which is larger in diameter) opens, and exhaust gasses seeking the path of least pressure take the easy way.....the intake port "exit". This is not a good thing because besides turning the intake port black "reversion" also contaminates the intake charge with inert gasses which will not burn again. My studies showed a direct correlation between low lift intake flow and reverse flow.....The better the low lift flow on an intake port, the better the tendency for reverse flow, or sucking exhaust. I designed my intake ports to not flow worth a **** at low lift, and also to not flow backwards. I'll not detail how, but the approach to the inlet valve seat, and its blend to the chamber are how it's accomplished....remember the seat is only the 45 degree angle that's ~ .055" wide. were not talking about the seat ring itself. The assymetric shapes I developed for that area and the last .5" of the intake port (the wierd valve job) are why the port doesn't dare flow backward, and as for low lift flow......study the piston velocity when the valve's at .150" or less. You'll find that it's so slow that the port's not being sucked on at all(relatively speaking), so big flow #'s at low lift wouldn't do you any good anyway. If I had known how to design an intake port that flowed 0 cfm. up to .150" lift, I would have, but all things considered my "weird seats" worked well for their time.
Exhaust ports: Read my Re. to RX first. I've never had much luck with performance of engines with no exhaust valves, so I've never been inclined to design exhaust ports without valves included. All I'll say is that the some flow attaches itself to the head and stem on the exhaust side, so the valve is somewhat like a guide for flow. The thing you're missing when flowing with no valve is that the valve stem represents part of the cross sectional area of the port, and, as previously stated areas are critical when dealing with velocities over mach 1. My port phylosophy has always been to calculate how much air a given displacement engine needs to run at a given rpm range (taking into account the many variables such as bore / stroke / rod length, and of course rules), and design a high velocity intake port that's not too large or so small that the velocities will cause separation of a well prepared air / fuel mixture.
Larry Widmer.
