Airflow after Overlap

Airflow after Overlap
By Don Terrill (c) -

"I pick up the .300, .400, .500 numbers and the car goes 1 tenth quicker!!!!!!!!!!! and the experts say no!"

I received this email from a racer who has spent his entire adult life trying to prove that mid-lift flow is the most important.

What I want to know is who is he arguing with? Who ever said picking up mid flow doesn't help?

The only lifts where you can MAYBE have too much flow is any lift where both valves are open at the same time - overlap.

My problem has been people saying the reason they focus on the mid numbers is because the valve spends more time there - it has to go through those lifts twice they say.

Sounds good, but when you do the math it's not true - it may go through there twice, but it doesn't spend much time there because it's the fastest part of the lobe.

If you look at upper lifts, the valve actually has to slow down, stop and change directions, which takes a lot of time.

Rule of Thumb:
Any increase in air flow, efficiently obtained, after overlap is good. Efficiently means highest cfm/ of port area.

Want to send off a nasty email about how wrong I am? Well, first read this and then write your own article.