THIS IS WHY YOU DONT BUY HEADS BASED ON FLOW NUMBERS.
Sorry for yelling but we should all know by now there is more to horsepower than just a flow number. Several big named engine people took a bunch of heat for fudging numbers by flowing a head at say, 20 inches and then do math to say the head flowed X amount at 28 inches. The problem is, and guys who use flow benches KNOW this, is that changing the test pressure and doing the math never adds up. I'll give a simple example.
Let's say you flow your head at 25 inches. It flows 265 CFM. You want to compare your port to the standard 28 inches, but you don't have a way to test the head again. You take the CFM at 25 and multiply it by 1.06 to get what the head SHOULD flow at 28. So 265 times 1.06 is about 281 CFM.
The problem is, that when you put the head on the bench at out 28 inches to it, it will loose a percentage. It won't actually flow what it mathematically should. As the spread between the test pressure goes up, the percentage of difference is greater. The more the head flows, the bigger the deficiency is.
Superflow used to publish the formula and a chart to do the math from one test pressure to another. I used the 25/28 inch number because I remember that number off the top of my head.
