Here's a question with a couple different scenarios.

1. A 350CI motor. At .500 lift how much HP are you gaining if your flow is say 240CFM vs. say 250CFM. How much power does that translate to at the wheels, all other parts being the same in both cases. What does that 10CFM buy you?

2. Same scenario, with a 383.

3. Same scenario with a 421.


Thanks in advance......

 

1. Based on the question, one would have to make a ton of assumptions. First, how can one figure how much power will come from a change, with no baseline given? Will the rest of the engine be optimized for each of the flows? Assuming 100 VE, 250/240 = 1.041666. About 4%.

2. Same answer as #1.

3. Same answer as #1.

4. How high is up?

RACE ON!!!

 

4. "How high is up?" Ask me around Mid-night and I'll give you an answer.....maybe

 

So it's directly proportional based on your 4% number? a 400HP motor will recognize a straight 16 HP gain, or are there losses that would drive that down to something less than 16HP

Also, if I may inquire, at what point does flow become subject to the law of diminishing return?

I am pretty sure that 10 CFM gives much more of a result between 180 an 190, but not so much between 260 and 270.

Any idea when the diminishing returns kick in for the listed displacements?

 

Dude, youre killin' me

 

What? I'm serious. All this talk about flow I must be missing something. I'm trying to learn.

 

 

So Vader and CFI, you're saying that flow rate in a vacuum is pointless.

Let's take some common mods. We'll use mine as I am familiar with it, and I know Vader is the Super Ram Guru.

Let's say there's a Super Ram, Long tube headers, and a 74219 cam.

Basically, a street build that you can still run A/C, pass emissions, doesn't shake your fillings lose at a stoplight, but also be in the 12s.

As far as how high is high, I say 10,000 feet is better than 5,000 feet.

 

 

i do not agree with the 4% rule but here is my theory behind cfm a 10 cfm boost should yield approximatly 20 hp should be double the cfm number is but that is in a perfect world
let me explain if you could max out that head at 250 cfm compared to 240 cfm it would be 20 hp you can also over pull that 250 cfm also so the gain could be more but on the other hand you might not be able to use that whole 250 cfm and your gain will be less confused yet
just because you have a head that gained 10 more cfm means absolutly nothing unless you can use it period case in point i think it was car craft who did a 454 bb vs a 454 sb the heads on the sb flowed something like 270 cfm out of a 220 port where the 454 bb head flowed 340 cfm out of a 320 port and the sb beat the big block everywhere across the board now this was on a pump gas motor it proves the bb could not use all that cfm and the sb made better use of it now if they upped the comp and cam choice to the 7600- 8000 rpm rang then that bb woild have spanked the sb azz because only then the bb would have been near maxing out that port
same is true if you take a low comp 383 and put a head on that flowed 350 cfm it wouldnt get out of its own way now just change out the pistons and valve train to max it at 8500 rpm and watch that thing fly
the largest motor available will have the best chance at maxing out a said head and that is why the larger motors usually run better
easier to error on the combo and still be fast hope this helps you out and doesnt confuse you more

 

Amazing! Twenty lines of off subject ramblings and not one period or capital letter. That makes it really hard to follow and understand. As best I decipher, you are talking about being able to use or the affect of changing heads for those with a greater cfm flow potential. That wasn't the question. The question was:I stand by my initial answer. If you increase the amount of air the engine ingests, not might ingest, not has available to ingest, not the difference in head flow ratings, but as asked, "if your flow is " by 10 cfm (4%) and accompany it with the proper amount of additional fuel, you will realize the 4% gain of 4% more potential energy being released from 4% more fuel. It could hardly be any more basic.

Not in racing!

RACE ON!!!

 

Diminishing returns come when you spend the $$$$$ for 10 CFM! I'd have to say you'd never notice the difference.

 

There'd be gains at a 10 CFM gain at .500" lift; as jsup posted the question. But keep in mind, the case would often be 10 CFM gains at lifts from .100" on up. That adds up on top, and greatly affects the bottom-mid range as well.

 

cfi efi you just can not comprehend enuf said

 

What corkvette is explaining is exactly correct - and deals directly with VELOCITY of the air charge. The airspeed of the incoming charge is more important than the actual flow number itself.

As corky explained a head that flows 270cfm on a low compression say 350 motor, will not have the same or as high velocity as a 270CFM head on a 406CI motor. The 406 is going to PULL a lot harder on the head and create a lot more velocity, therefore make better use of the head. A "lazily" utilized port, regardless of a good number will not make good power. If it did then we would all be running the LARGEST port they could make with in the envelope of a SB head and the CFM would be well over 400CFM!

A good head porter will make the VELOCITY of the port match that of the engine size, and not worry about CFM numbers. Giving up a few CFM to gain 10% velocity will yield a much better head/performance.

The magazines can't easily measure the velocity or moreover relate that to specific motors - so CFM is what they like to talk about.

Now to get more direct to your question - 10CFM in an apples to apples comparison were the heads are "pulled - on " by the motor and create a good velocity - then you will see about 2hp per CFM. But as i always say the proof is in the pudding!

 

Jesus!! Find the space bar, the period and the shift key!!

 

Thanks guys, I'm following this. Thanks for the info.

 

"enuf said"? I have to admit, following the non-punctuated, non-capitalized run on compilation of words isn't easy to understand, but I was able to decode "enuf" (sic) to see that you were going on about flow velocities, etc. Comprehension would be easier for all, if you wrote in a more comprehensible manner.


Jesse,
You too.
Even being correct, you and he are off the subject. Reread the question. It doesn't ask what happens if you install heads that can flow more air. It asks, "At .500 lift how much HP are you gaining if your flow is say 240CFM vs. say 250CFM.?". In other words, if you stuff air into a cylinder (engine) at a rate of 250 cfm, rather than the previous 240 cfm (a 4% increase), "What does that 10CFM buy you?"? Get it, now?

RACE ON!!!

 

CFI - not real sure why you are jumping me? I have not a dog in this fight and just trying to help the guy out. I never said you were wrong.

And the way I read the question is yes for #1 question you are right with the way you interpret the question.

However the way I answered it - DEPENDS on the motor you stick the heads on. As the question is laid out, as you increase the CI, you are also putting more air demand on them, which is going to increase the velocity of the incoming charge. As a result, you will have different results/effects at different engine sizes. A 421 CI motor is going to have a LOT higher velocity than a 350 of equal compression etc. As a result you get what I was explaining above.

Again a good head builder is going to optimize the port size, PR pinch area and throat all to obtain the max velocity....translating that to this question you will get varying results at these different CI motors he lists.

In other words, the results will vary.

 

Since you're interested in air-flow, here's another example you might find interesting. Hot Rod Magazine-March 2008-427 LSX. This is an LSX block, 4.125" Bore-4.00" stroke-11:1 compression-Single plane intake-950 Holly. Made 552 TQ @ 5000 & 594 HP @ 6400. Same bore and stroke as the popular 400" SB Chevy with a 4" stroker...427-434". Makes about the same power you'd expect from either engine, with those specs and parts mentioned above. Here's the kicker...the LSX does it useing a cam with an intake of only 211* duration, .591 lift. Exhaust is 230*... small. It would take 240*+ duration with real good heads to hit those numbers useing a SBC. It's the flow of those LS7 heads that does the trick. Air in- BANG -air out.