Port velocity average target fps?

Phreakish said

It's always the same game, it never goes anywhere.

To get an average fps air speed you can take the flow rate in cfm, divide by 60 to get per second and then divide by the csa in sq ft. There's 144sq in per sq ft.

So if you have 300cfm and a 2.0sq-in port, you have 5 cfs (300/60 = 5) and .014 sq ft of port (2/144 = .014).
5/.014 = 357 ft/s. Obviously I just made up the numbers, but the same can be done with any data.

This is just rule of thumb of course, but it will hold at any given cross sectional area. There will be local high and low velocities of course, caused by the interaction of the boundary layer and wall inflection.

Click to expand...

I played around with your formula, works out Chad's formula is a simplified version, cfm x 2.4 / csa = average fps. 144/60= 2.4 now I see where his constant comes from was wondering that.

Basically a 6683 rpm 367 cid engine needs 300 cfm and a 2.25" csa giving an average 320 fps according to their formulas.

Question is, is that an acceptable fps for a street strip my guess it is, but to get the fps to where Eric says it should be 285 fps would need to be a 2.53" csa. But funny as he said 285 fps should be the goal and one of the heads he was comparing calculated to be that but actually speeds were way higher then that leading to believe there actually average was way higher.

I'm not overly worried about it, obviously we only got a few heads to choose from anyways.