cfm =horsepower

is there a rule of thumb ,that with ideal conditons. a certan amount of cfm added equals(x) amount of horsepower?

The very general average is roughly 2hp per cfm. I say very general because I know of many engines that exceed that number by a bit, and a bunch that never reach it. It's hard to say because the bench results you are using are fairly subjective anyway. A good bench with "stingy" numbers may lead you to think you're making more power with less, and a generous bench may lead you beleive you are not making what you should.

On a motor with a well designed head, it is possible to reach 2.45 hp per cfm in a high hp buildup. 2.3 hp per cfm is more likely though, and pretty stout performance on a bigblock type build. My 528 makes about 880 hp, and has a headflow of 368 cfm at .700, the highest even number where the cam actually lifts the valve. There are so many variables involved that this number can't be taken too seriously, it is just a rough benchmark.

Bigger is not always better( CFM & AIR SPEED )

These are great time wasters, and like most calculators, completely ambiguous. http://www.wallaceracing.com/calcafhp.php

I've found that on the type of motors I build (moderate perf motors) that 2 hp per cfm is a good rule of thumb. I just finished up some back to back dyno testing of intake manifolds and a 50 cfm increase in flow was good for 100 hp.

it gets hard to nail down cfm to hp relationships because it depends on what parts or circumstances you are talking about, 2hp/cfm is a general rule,, at 28".

on nhra stock eliminator cars its more of a gain because the heads flow so poorly, they are more restrictive to the displacement and accleration of the engine. they see more like 3-4hp per cfm.

also,, on an engine like a stroked small block or big block,, a 20 cfm gain will result in more of a power gain than on a std stroked or smaller engine due to the head being more restrictive to the larger engine.

jeff

I've seen as much as 2.52hp per cfm, that was on a 362" Super Stock motor, the Layer heads flowed 240, motor made 605hp.

yep, what they said. Its an ez formula and will get you very close.

Try this DUSTIN,mildly built,.257*cfm*8=hp all out,maxed built .300*cfm*8=hp, just decide what numbers you like best,its all a est till you get on a dyno or track test it all anyway.

[quoteI've found that on the type of motors I build (moderate perf motors) that 2 hp per cfm is a good rule of thumb.

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This was real close to what my engine made.Dwayne flowed my SR`s as they came from MM they came in at 309cfm with a std port opening. When it the dyno the result was 617hp.