SS02G

Ok so I'm currently in school to achieve a degree in motor sport development anyways my prof. Touch briefly on how head flow can be used to directly determine peak rpm and hp/tq. Can you "hardcore" guys give me a good conversation on this and does anybody have a formula that will give me the answers to peak rpm and peak Hp/Tq? Let's say that the head flow hypertheticaly is 300 cfm intake 280 cfm exhuast and let's say on a 350 ci ls1 and a 427 ls1 just for kicks um... Any other numbers you guys need to help me understand this concept just plug them in where needed. Hope someone can help me because we're not goin to cover this till after the winter break and my curiosity is gonna kill me lol thanks guys Marcus

Old SStroker

Change schools, or at least profs. Did he also say that high performance heads need to have high velocity and really good low lift flow? It wouldn't surprise me if he did. My guess would be that the prof is not a well-known and successful head porter or engine designer.

Here is a 4-year old quote from a great head porter and engine guy, Larry Meaux:



"Peak_HP = Flow_CFM * .257 * Number_of_Cylinders

This is the estimated potential Peak HP to expect.

You multiply 87 percent (.87) times cam's theoretical max lift , round off to nearest .050" in Flow Test, then see what CFM is at 28 inches of H2O.

example=> .700" Lift cam:
.700 Lift times .87 = .609" Lift
Flow head at .600" Lift , then take CFM at 28 inches and calculate HP potential with above formula.

.257 Factor = for beginning engine builders and engines near 10.0:1 Comp Ratio

.285 Factor = would be for Professional engine builders with wet sump pans, lightweight rotating assemblies, low tension great sealing rings, deep oil pans, etc. and excellent use of inertia/wave tuning with 9.5 to 11.5:1 Comp Ratios or 11.5 to 13.0:1 CR ranges without fully utilizing inertia/wave tuning effects

.300 to .310 Factor = Current ProStock Technology with dry sump, unlimited carburetion, High Comp Ratio, ultra lightweight rotating assembly, etc, and maximum use of inertia/wave tuning, etc, 14:1 to 17:1 Comp Ratios.

(usually no better than .3200 efficiency or no worse than .2980 eff %)"

Please notice that it isn't an simple one-factor formula, and that displacement is not mentioned, nor is torque. Does that imply to your that measured head flow relates to power and not torque? Hmmmmm.

If you simplify Larry's formula (assuming an 8 cylinder engine), for the magic number your prof wants, you get: Peak HP = 2.056 x CFM @ .87 x max valve lift. That's using the .257 factor x 8 cylinders.

Let's say you were building a fairly normal engine with .575 lift that you wanted only max power, and you got a really good set of heads from Larry that flowed 250 CFM (@28 in. H2O) at .500 lift (.87 x .575). A good builder could then expect 2.056 x 250 or 514 fwhp. That's probably not unreasonable.

These really good Meaux heads might flow 300 CFM @ .600 lift, so using .690 valve lift, which is probably not for your Daily Driver, you now may get another 100 hp. (617 fwhp). Again, not unreasonable.

Now lets say these same heads keep increasing flow with lift to 340 CFM @ .700 lift. That means valvelift in the engine would be about (.700/.87) or a tad over .800. That's really a track only engine, but now it might make (2.056 x 340) or right at 700 hp.

It gets even more fun when the "Factor" changes. With a.285 Factor, the .800 lift engine suggests 775 fwhp, and the .300 Factor engine builder might look for aboout 815 fwhp.

Those same heads then have a potential of from 514 to 815 fwhp. If you only look at the max flow of 340 CFM would your magic number be 1.51 hp/CFM or would it be 2.40 hp/CFM?

WARNING:
If you use any of this and DON'T give full credit to Larry Meaux, I will personally sic the Alabama arm of the "Family" onto you. You can run but you can't hide from them.

Now if your prof isn't expecting something this complex, which is how the real world works, you will either get an A+ or a D-, depending on how smart (or dumb) the prof is. My guess is that you'd get the D-.

If you figure he just wants (and has secreted away) one magic number, you might use 1.96, the rounded average of the 1.51 and 2.40 numbers. You should probably have a good, easy reading reference for that number. You can probably find one. Google is your friend.

On second thought, if you disagreed with the prof or showed him up in class, you would probably flunk the course, so you need to decide if grades are more important than knowledge. That is actually a very good life lesson which many never learn.

Pardon me while I step down of of my soapbox...

Jon

EDIT: Homework assignment. Using the fictitious heads in the above example, would they have the potential to make more horsepower on a larger engine (say a 427) than on a 355? Why? Assume they would work on either engine.

Second part: Which engine would make more maximum torque, and why.

SS02G

ok cool man that makes sences i think all he was doing was just teasing us on how you can come up with "hp" from head flow with out actually building/dynoing a motor but please take the mic i want to learn everything that i possibly can from anybody and everybody and you explained that nicely ive actually been looking into attending SAM (school of automotive machinists) cuz honestly i hate the other class like eng. hist. well you get me any way so how bout rpm i mean there has to a point that air will just stop "walking" in right and lets say no valve float or anything like just the physics of fluids

LS1-450

iTrader: (33)

Thank-you

KMS.1320

iTrader: (1)

Jon,

What if the heads flowed less than 340 CFM at .800?

Would you still use the same numbers to judge theoretical max lift? or would you just keep lift below the stall point and call that the max?