bigchief

i found this website because i wanted a quick way to see the maximum amount of hp i could make with a set of heads that flow these numbers: 62, 140, 203, 239, 259, 256. heres the website: http://www.bgsoflex.com/flowcalc1.html
its just that i dont see my hp coming up correct, what should i be typing for Test Pressure for CFM Measurement

sofakingdom

iTrader: (1)

Whatever those numbers were obtained using.

In general, with flow numbers at 28 in Hg, the MAXIMUM THEORETICAL HP you can get out of the heads will be about 2 times the flow numbers; or in that case, about 500 HP. The exact amount will depend on all sorts of other things; compression, BSFC, material the heads are cast from, cam properties, exhaust, etc. etc. etc.; but that will give you a rough idea of what to shoot for. Don't believe this "2.165 HP/CFM" type of crap, because there's WAY too many variables. Trying to "calculate" it down to that kind of precision is a "measure with micrometer, mark with chalk, cut with axe" situation.

F-BIRD'88

This simplified formula is used and promoted by AFR.

.2575 X cfm@28" X number of cylinders = max hp.

To find how much power you can realistly get at a streetable compression ratio, I use the 90% rule. Multiply the AFR airflow/cfm formula result by .9.

So a head that flows 259cfm should be good for 480hp at a usable 9.5-10:1 compression ratio.
This assumes you have a correctly tuned motor with a big cam, good intake, headers etc.
You may exceed this on a very well built motor by employing all the dirty tricks, but, not by much.