Cylinder Head Porting and Power Production

MOPAROFFICIAL said
Yes there is only so much time you want to hang the valve open into reverse/backing up and thats where a dyno is handy.
While the bench will show it backup...'holding the valve open like a refrigerator door', in the engine at micro blips of extreme pressure... its different.

As for average flow.
A long time ago when I first got my flow bench I always wanted to see what CFM got through with a valve that was just opening and closing as fast as i could....but its not a running engine with a speed of sound pulse. Fwiw a head doing 250 peak by.500 held 202 cfm doing that. We try what we can. That head @.400 flowed 224cfm

I think an often missed opportunity to fix port issues with turbulence and such, is the intake manifold.

I’ve seen some intakes just kill a head, some do nothing and some do the most important thing I’ve found...a good intake manifold, properly prepped can correct what looks like a break over or backing up issue. You may not see an increase in flow, or maybe even lose some air flow.

But a good intake will settle down the port. You can see it on the manometer. And I’ve seen it (mostly with tunnel rams but I’ve had a couple of single 4’s do it...but they took a bunch of welding and grinding) eliminate the break over. Even testing at pressure drops above 28 inches.

That’s why I never base lift on what the port does as far as backing up or breaking over. A good intake will fix that, or make it so minute that cutting back lift is just a power loser.

Along that line, seat angles matter. As I’ve said before, I really don’t see a need to do any real performance heads with a 45 any more. Yes, low lift flow will be less. But the SHAPE of the seat and valve will be much more beneficial than getting more curtain area. It’s about shape and air speed.