Cylinder head CFM to HP?

[Steve.k]

The engine I’ve been working on is at 1.97/hp per cfm. Trying to kick over the 2.0 as we speak. Heads flowed in 385-400 range.

[digger]

FWIW, a lot of work w/ my own copy of EA Pro and collaborating with someone who had a reasonably current version of Dynomation using the same data (mine for the then build-in-progress) reinforced some beliefs that I've had from a good bit of running EA Pro using real-world data and results I'd seen from a predecessor of Dynomation:

EA Pro
- Required a lot of gaming the inputs from the actual data in order to generate baseline results that matched my engine dyno data "reasonably well"
- Even with all the mods to the inputs as noted above, the sim always over-estimated peak torque output and underestimated peak HP RPM by 400-600 RPM
- The general trends were realistic, but the outputs were far from being able to take at face value

Dynomation
- Almost always said the engine would perform better with a wider LSA cam, despite real-world testing to the contrary
- Was better at predicting peak HP RPM, but way over-estimated the peak HP #

Neither was that great, IMO. Or maybe something about a standard-port BB Mopar doesn't "fit" the traditional SBC model I suspect these programs are correlated against. Doesn't matter, I'll trust what I see from a reputable engine dyno w/ an experienced operator. I've relegated these "affordable professional" sim programs to one step above toys. I don't think my budget can swing any program that would actually give me legit outputs for actual inputs. My PipeMax v3.98 (IIRC) was a much better bang-for-the-buck in terms of providing me w/ valuable data to factor into my build.

Re the 2 HP per CFM "rule of thumb"... you know what it's still good for? If someone says they're going to build a 700 HP NA engine with 280 CFM heads, I know they probably "can't get there from here", unless we're talking about a high-end engine development program. And when I see someone builds a combination with 340 CFM heads that barely breaks 600 HP, it's a pretty good indicator that combination isn't well thought out in one or more areas (too much port volume for heads, etc.).

Naturally, JMO and JM $.02.

Yeah I do not recommend EApro it is rubbish .

I would use engmod4t and I would focus on learning how and why things work and the interrelationships that will help you see the engine as a combination and not a sum of individual parts

Sorry I cannot agree there i have an engine shop where we are fully equipped with dyno etc. I have built countless engines using pipemax and EApro and have been within 5 hp on every build. You just have to work out some of the parameters that are wrong and adjust them accordingly.
So no it is not rubbish.

EAPRO exhaust modelling is garbage it even essentially admits that in the help manual it has the simplified collector and detailed collector models. You make a variable change on exhaust and dyno test you don't get remotely the same trend, infact you get the opposite. Do the same in ENGMOD4T and you get the correct trends as tested. When you interrogate the pressure waves EAPRO is clearly wrong.
I'm sure if you have a pushrod v8 you can fudge the power and torque numbers to match whatever you like......

[smeg]

I use it to design engines and it works all of the time, you use it and it doesn't work. I don't know what to say.....

[BradH]

I use it to design engines and it works all of the time, you use it and it doesn't work. I don't know what to say.....

Not sure if that was directed at myself or "the other guy". Regardless, you build engines for a living and I work in software development by day, and am a gear-head (petrol-head) in my free time. My perspective -- given how I earn my paycheck -- is that the simulation software must include some key logic deficiencies or invalid assumptions to generate results as far off as I've seen for my personal builds.

[David Redszus]

given how I earn my paycheck -- is that the simulation software must include some key logic deficiencies or invalid assumptions to generate results as far off as I've seen for my personal builds.

In your business, there is a phrase quoted directly from the bible; "Garbage in = garbage out."

While some engine simulations are empirically based and do not follow the laws of physics (or computers) many output errors are the result of input errors, incorrect units, and other assorted crimes.

A good simulation program is carefully validated against dynos testing; dyno testing may introduce its own error set.

[BradH]

GIGO, indeed...

Misinterpretation -- or misrepresentation -- on either side of the equation and it all might as well get tossed out like yesterday's kitty litter.

[tuffxf]

Gday,
As for the original question
On our engine, 2.22hp/cfm, probably a tad more there if we chase it
Cheers

[PRH]

Brad has two different engine sims....... that when loaded up with the same inputs....... (without any fudge factors being applied)....... spit out different results.
They can’t both be right.

And neither of them matches actual dyno results.

[David Redszus]

Does anyone have access to the equations used to convert CFM to power?

If so, please post or PM.

[BradH]

Oh... you mean re-align the discussion w/ the original topic started 15 years ago?

(My apology; given the general circumstances we're all living in these days, I try to find humor where I can )

[PRH]

Other than the ones posted earlier in this thread?

[BradH]

...

And neither of them matches actual dyno results.

Thank Gawd the dyno results have correlated so well w/ the car's on-track results... or I'd be totally f***ed.

Oh, wait, I gotta a new engine to test.

[digger]

Does anyone have access to the equations used to convert CFM to power?

If so, please post or PM.

no such animal exist (to do it properly that is) i'm sure the superflow manual has a "rule of thumb"

EDIT: Superflow

https://superflow.com/wp-content/themes ... Manual.pdf

Hp = 0.26 x cfm@28" x # of cylinders
Hp = 0.43 x cfm@10" x # of cylinders

Peak hp rpm = 1196/(CI/# of cyl)*CFM@28"
Peak hp rpm = 2000/(CI/# of cyl)*CFM@10"

[David Redszus]

Other than the ones posted earlier in this thread?

There are no scientifically correct equations posted on this thread. CFM cannot be converted to HP.

The are "rules of thumb" which are practically useless unless applied to almost identical engines with a high
degree of similitude.

As MadBill indicated, the displacement factor is missing.
So is compression ratio, rpm, fuel ratio, and a number of others that are needed.

Most important is air mass, which determines how much fuel can be burned and how much energy can
be produced.

As has been said many times. "correlation is not causation" and certainly not prediction.

[maxracesoftware]

by David Redszus » Wed Dec 16, 2020 5:31 pm
CFM cannot be converted to HP.

David ,
your comment : "CFM cannot be converted to HP." ... seems strange ?

i must not understand you actually mean !

CFM , ACFM, and especially SCFM can all be converted directly into HP.

all the necessary equations are in SuperFlow's older SF-901 WinDyn manual

_______________________________________________________________________________

Engine CFM or SCFM is easy , or ( total induction air density to HP is very easy to calculate )

Total Induction Flowbench CFM is a little harder , but still has exact direct relationship to HP

both have exact direct relationship , that is , total induction CFM to Peak HP or ( total induction air density to HP )