What is up with using head flow in cfm divided by port volume in cubic centimeters as a figure of merit (I think it was refered to as port efficiency)? That produces a constant scaled in 1/time, which makes no sense. Are they trying to get something akin an orfice coefficient? Or is it supposed to be an indicator of velocity, but using volume instead of area, since it is easy to measure volume but hard to compute average cross sectional area of a port? Or ????
Inquiring minds want to know ...

 

Nobody has any thoughts????

 

Thought 1: Who is suggesting this? How about a link.

Thought 2: For a given port length, the port volume is effectively a measure of average cross section (Divide volume by length) so you are comparing flow thru a certain average size hole. Think of it as a unitless factor.

So 250 cfm/250 cc = 1.00 and 300 cfm in a 200 cc port would be 1.50.
This says a higher "Port Efficiency" factor would also be a higher velocity port. Realistically you probably wouldn't see much near 1.50, nor near 1.00 in a ported head. I'd guess 1.2 to 1.4 would cover many SBC ported heads.

Thought 3: By just using one (max) flow figure this comparison doesn't say as much to me as area under the flow curve.

Thought 4: Comparing heads this way probably isn't a bad idea, but I wouldn't suggest using it to choose you heads.

 

One of the head vendors from the right side ...
That was one of my thoughts. Calling it "port efficiency" rather than velocity is strange in that too much velocity is harmful (that is why we port, right?), but a stock port might have a "port efficiency" better than a head that makes much more power.
My thought too.
Pretty much what I was thinking ...