Guess that makes 2 of us. Here's Larry discussing some of his stuff on another forum.


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 [censored] at low lift, and also to not flow backwards.


Its obvious that if you can create enough inertia early on in the intake cycle then it will continue well past BDC. The irony here is some engines need more exhaust residual to improve the burnable mixture by increased vaporization so airflow dynamics are one thing and the chemistry of the burn is another.

Are you familiar with UDHarold?


At low engine RPM, an early exhaust opening HURTS bottom-end power. It could extract more torque from the crank, instead of blowing power out the exhaust pipe.
At low engine RPM. an early exhaust closing HELPS bottom-end power. It helps prevent reversion from contaminating the intake, and reduces fuel loss during overlap. At low-RPMs, it is the TIME of the exhaust overlap, not the number of degrees it has.
At high engine RPM, an early exhaust opening HELPS top-end power. The most important thing becomes the necessity of cleaning exhaust gasses out of the cylinder, to allow the maximum intake charge to get in.
Peak engine horsepower occurs when the exhaust cam can no longer let ALL the old exhaust gasses out, and some remain to hinder cylinder filling.
All these things occur with the intake on the same ICL.

I remember Larry Meaux discussing a Hemi engine once that had the most VE he had ever seen on his dyno. The problem was the intake charge was heading straight the exhaust port so it wasn't reflected in the power it was making or should have been making had it been contained in the cylinder and utilized.



Just more stuff to think about.