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#32855 - 12/24/06 07:19 AM cfm =horsepower
mcat4321 Offline

Registered: 08/04/03
Posts: 3013
Loc: cincinnati ohio
is there a rule of thumb ,that with ideal conditons. a certan amount of cfm added equals(x) amount of horsepower?

#32856 - 12/24/06 07:23 AM Re: cfm =horsepower [Re: mcat4321]
moper Offline
I Live Here

Registered: 02/03/03
Posts: 12675
Loc: Columbia, CT
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.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.

#32857 - 12/24/06 07:38 AM Re: cfm =horsepower [Re: mcat4321]
gregsdart Offline

Registered: 01/21/03
Posts: 8462
Loc: Frostbitefalls (Rocky&Bullwink...
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.
Educated at SHK U
Measure with yardstick
mark with chalk
cut with torch!

528 cubic inch alky injected 440-1 wedge, 3055 race weight.
8.779 at 153.16 mph. 1.289 60 ft. density altitude 1617 feet. Best 60 ft 1.24

#32858 - 12/24/06 07:50 AM Re: cfm =horsepower [Re: mcat4321]

Bigger is not always better( CFM & AIR SPEED )

#32859 - 12/24/06 08:13 AM Re: cfm =horsepower
dthemi Offline

Registered: 10/31/04
Posts: 2787
Loc: back in Georgia
These are great time wasters, and like most calculators, completely ambiguous.

#32860 - 12/24/06 11:21 AM Re: cfm =horsepower [Re: mcat4321]
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 24952
Loc: Oregon
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.

#32861 - 12/24/06 02:26 PM Re: cfm =horsepower [Re: AndyF]
moderncylinder Offline
top fuel

Registered: 10/30/04
Posts: 1752
Loc: detroit area
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.


#32862 - 12/24/06 02:35 PM Re: cfm =horsepower [Re: mcat4321]
LSP Offline
super stock

Registered: 08/19/03
Posts: 1196
Loc: Charlotte, NC
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.

#32863 - 12/24/06 02:39 PM Re: cfm =horsepower [Re: moderncylinder]

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

#32864 - 12/24/06 04:35 PM Re: cfm =horsepower [Re: mcat4321]
572daytona Offline

Registered: 09/03/04
Posts: 107
Loc: alabama
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.

#32865 - 12/24/06 07:05 PM Re: cfm =horsepower [Re: AndyF]
Dap Offline
top fuel

Registered: 01/20/03
Posts: 1855
Loc: Staten Island N.Y.
[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.

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.
10.084 @ 135.21 mph N/A through chambered mufflers,3300lbs. Stock stroke wedge

#32866 - 12/25/06 11:10 AM Re: cfm =horsepower [Re: moderncylinder]
Cab_Burge Offline
I Win

Registered: 08/23/03
Posts: 31677
Loc: Bend,OR USA
My 9.25 to 1 comp. ratio 512 stroker 400 block motor made 612 hp at 5000 rpm on pump gas with a set of ported "906" that flowed 266 cfm at .600 at 28 inches.That is 2.3 hp per cfm, I was very happy with that. Your results may vary.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

#32867 - 12/25/06 01:20 PM Re: cfm =horsepower [Re: Cab_Burge]

What i don't understand is why SB guys think that they have to have heads that flow over 300cfm to get any power. The BB guys heads flow the same, if not worse....Whats the deal?

So lets say 300 at 600 with over 200 at 300 lift. that would be maybe 2hp per a big block will get alittle more out of that...but theres over 100ci there. Im just rambaling now....



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