Since that last thread was locked, and my question was not answered, I thought I would make a post about CFM in regards to making horsepower, and how much CFM is needed!

Please if you don't know what your talking about, or don't have any experience then please lurk all you want.

It is very noticeable that Jsup, and others which includes myself have been chatting back and forth about cylinder heads.

I have been hearing for years, and reading that for every 1 CFM equals roughly 2 HP. So if you have a head that flows 250cfm, then the max HP with a naturally aspirated motor is roughly 500hp. And if you have a head that flows 310cfm, then the max HP with a naturally aspirated motor is roughly 620chp.

Is there any relation to cfm and horsepower? I dont know if it's an exact science or not, but I do know that cfm does make power. I just don't know if there is any calculations.

I am sure members like Deakins, or better yet Tony from AFR have the answers. Also if anyone has any experiences with changing heads, and knowing the flow #'s, and what power gains, that might help as well.


Note: Jsup if AFR is mentioned, just relax man! This thread isn's about you. This thread is for learning purposes.

 

That is totally theoretical power increase. I can tell you that recently I modifed a customers 90 C4 that had a 383 installed in it a couple years ago. They used a set of Edelbrock Performer heads and had a small flat tappet camshaft. I replaced the Edelbrock heads with a set of the latest AFR 195 eliminator heads and a Accel Super ram intake, and a 219 camshaft. I gained almost 70hp to the wheels with this combination over the baseline of when it came in. Did you ever get your engine built?? It has been a couple years now hasn't it?

 

speedtalk.com

to many variables

 

Heh man. I just e-mailed you. It gained almost 70rwhp? I think I know the car you are talking about. You mentioned it a while back when I talked to you. I was supposed to get a 383 built, but I got screwed over by the engine builder. I am getting a 421 built. Jim has finished the shortblock, and Tony is almost done the Eliminator's.

Things are tight money wise, so I am doing it, bit by bit. My wife is on track to get induced on Friday, so life will start to get real busy after that point. We are having a little girl, and I cannot wait!

Nice hearing for you. Those AFR's you mentioned. Comp or Street Port's? 70 rwhp is huge! What rwtq did it gain?

Later man!

 

Let us know!

In the next future.... you'll need to forget about CFM... you will be forced to learn about "others Flows"..

The 1 CFM = 2 HP probably is a good equation.

If you have an intake that flow only 200 CFM , and if you have a head set that flow 250 ... this equation can't be applied.

 

waaaaayy too many variables

 

Well the whole problem that we will run into is hp is a function of essentially where you are producing your torque (the higher the better as far as hp is concerned). There is so much involved with how the engine makes power at different RPM levels that it's really difficult to put hp gain number along side of flow improvements. A lot will have to do with the FPS limitation of the intake tract (that is, how much total air can pass through the head before reaching too high of velocity; many engineers are going to a mass type measurement to represent more along the lines of possible consumption of air rather than flow). Depending on where the mcsa is located will change this; in the right area you can try to get it way up close to the limit (established by physics) and not have a problem, where as in other areas of the tract you will be presented with problems quicker than predicted.

Obviously the port that can handle higher velocities (fps) will allow an engine to pull more RPM (if the rest of the package is designed around that fact) and hence more hp even if the flow isn't any better. That doesn't mean that the VE of the engine is any better either (it may not be getting any more air), it's just allowing the unit to make usable power higher.

This is a very complicated question and people will generally fall on one of two sides; either they will be an experienced porter that has done a lot of grinding and testing, grinding and testing, repeated hundreds of times to develop their skill set, or they will be more from the academic community that does more work on paper before the grinding begins. Both make some very effective units; we just go about getting there a little differently.

With the example above; the gain is what one would expect. They changed out the three major components that will determine where the power is made in the RPM band. HP is actually easy to get if you really understand how to make it; my 355 makes well in excess of 600 hp... To do that it spins up to 8000RPM, not making all the much torque mind you, but producing a lot of energy none the less. I have run for now, I will check back later and see if I can add anything and see if anyone has brought up any good points that didn't think off or was unaware of.

 

This is the answer you are looking for:
If the engine is built correctly to optimize it's combination, a cylinder head with a certain flow number caculated from this formula (cylinder head flow at 28" of water X .258 X number of cylinder) can support "X" amount of power. This assumes the engine is built to maximize the combination, most combination will not hit the numbers shown by the caculation.

Example: 300 CFM at 28" could support 620 HP (300 x .258 x 8)= 620 HP.

 

Thanks bro!


Are you switching up the combo this winter?

 

So what did it put down overall in total?
It is easier to make a comparison; if the old combo made 300rwhp and the new set up made 370, that is OK, but if it went from 400 to 470 that is great!
thanks

 

Please see attachment. I was wrong about the hp gain, it was the Tq gains that was 70+ but still it gained just shy of 65hp over the original baseline curve. The numbers were: 322.8hp vs 258hp, and 388 ft/lbs vs 310 ft/lbs. And also this is a A4 car so the numbers are lower as well. So it was OK, but remember any time you gain nearly 70hp it is very good. The reason is that you can FEEL it with the old butt dyno, if you gain 15hp with a simplistic hand held tuner, you really can't feel it even though its measurable on the chassi dyno.

 

That graph clearly shows the TPI "brick wall". But it did gain significant TQ from just shy of 4000 through 5000 RPM.
Nice work.
Aaron

 

Hey Aaron how are things. Yes, its the traditional brick wall effect, we could have got more out of it if I had gone in and ported the SR and the intake, maybe another 20 or so. But in those ranges it probably would not have been worth the effort to do so. In any case the gains were significant, and the SOTP feel is good. When compared to my cammed up LS7 in my Z with ported heads and the other supporting mods that pulls like a freight train all the way to 7k, it isn't but a pittance, but then the LS7 is a totally different animal.

 

Tom,
I will have to agree with that statement. My brother just bought an '08Z and I have been looking, but tough to find a JetStream Blue Z for a good price. With the recent 30+% drop in auto sales over Sept '07, the dealers may be getting more desperate to deal. Who knows? For now, the LS2 is as close as I get to the smooth factory C6 performance.

Or I can go have some fun by taking out the C4 (it is now steadily using the full range of the 3-bar MAP).
Aaron

 

Tom, that does seem a bit soon on the HP peak.... most 350/383 SR/219 combinations I've seen make the hp peak right in the 5000-5500 rpm area. My old 383 actually made its peak at 5800 rpm, but I degreed the cam in a couple of degrees retarded... so thought it might be a little late.

I dunno...

 

He gained 25% more power with a baby cam and you gained 26% more power with a much "bigger" one. Sounds pretty impressive to me.

 

The only guy HIGHLY qualified here to answer the question and nobody listens. Deakins will teach you a thing or two if you're willing to accept that some of the popular concepts are bunk and keep an open mind. (no offense TJ, just Deakins holds an Engineering degree which I respect tremendously and has designed aircraft. He really knows fluid dynamics and how motors really work)

 

Lots-o good info here:
http://www.gofastnews.com/board/tech...t-volumes.html

Check out the rest of the articles in the numbered series as well.

 

I am not qualified to answer due to lack of mechancal engineering degree, and due to my limited budget. But, I would do what TJ and others recommend. Follow PROVEN combinations, dont waste money on R&D.

 

Talk about not reading the rules regarding hostility.