Rat Bastid said

I’ll post a link in this thread of about an hour of 3 of the best minds in the business discussing several topics, one of the longer ones being exhaust cam timing and headers and how they (together and seperately) affect the intake charge and volumetric efficiency.

Watch it because it should answer at least most of your questions.

I have been a proponent of reverse flowing the ports about 1 month after I bought my flow bench.

Any time you can reduce reverse flow in either port (even at the expense of flow in the forward direction) you will make more power.

Click to expand...

Rat Bastid said

Thats why when I can I use 50 degree seats. It looks like hell on a flow bench but they make more power. Everywhere. Even with less low and mid lift flow numbers.

Shape, shape SHAPE matters. And the shape of the 50 degree seat (done correctly which means you need a seat forming tool because a stone will not get you the same results) is better for flow at higher depression and it retards reverse flow.

To that end, not all 50 degree valve jobs are not the same. IMO, they need a full, sharp two angles coming off the seat, a .100 wide (minimum) top cut of 5 degrees (45 degree) for the intake and the exhaust wants a tight (relatively) radius right off the bottom of the seats (no angles) and a well defined .100 wide (minimum) top cut that blends right into the chamber.

Click to expand...