Flow numbers and max HP potential

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Cuda416

Cuda416

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I saw a video choosing a cam that claimed (in a general sense) if you take the flow of an intake port for a given lift, and multiply it by 0.26, that will give you the max theoretical hp for that cyl at that lift. So for magnum heads, that's 233 from the factory as far as I understand, so at that rate, each cyl should be able to support 60.5 HP, or a total of 484 HP. How far off of reality us that? I understand reality over theoretical but software can effectively predict HP based on such things so how far off is this?

Opinions?
 
Cuda416 said:
I saw a video choosing a cam that claimed (in a general sense) if you take the flow of an intake port for a given lift, and multiply it by 0.26, that will give you the max theoretical hp for that cyl at that lift. So for magnum heads, that's 233 from the factory as far as I understand, so at that rate, each cyl should be able to support 60.5 HP, or a total of 484 HP. How far off of reality us that? I understand reality over theoretical but software can effectively predict HP based on such things so how far off is this?

Opinions?
Click to expand...
Wow, 484 sounds like a lot
 
PRH said:
there should be a disclaimer.......

*For bench racing use only*
Click to expand...

Ha, well yeah, but this is AFR so I'm relatively sure they know what they are talking about? Also, this is for full on racing engines that see 7k etc.

Not arguing but I mentioned this to a math head I work with and his response "I would have thought it was 0.27 ish" and he explained it was something about the constant "e" (2.71828) divided by 10.

Again, this is theoretical (bench racing) so that "disclaimer" was mentioned. I just found it pretty fascinating.
 
I have beat that formula numerous times...... with builds that could have been improved to make even more power.
It is by no means an indicator of the “max” power than can be made by a given amount of flow.
 
PRH said:
I have beat that formula numerous times...... with builds that could have been improved to make even more power.
It is by no means an indicator of the “max” power than can be made by a given amount of flow.
Click to expand...

Really? You have gotten stock magnum heads, normally aspirated, to better numbers?

I'm not firing up a debate, just trying to learn something.
 
What I’m saying is, I have built numerous motors that have made more than what the .26hp/cfm forumla says is possible.

As with all builds...... one parameter isn’t going to define what the peak output can be.
 
PRH said:
What I’m saying is, I have built numerous motors that have made more than what the .26hp/cfm forumla says is possible.

As with all builds...... one parameter isn’t going to define what the peak output can be.
Click to expand...

Fair enough. I'm fully aware of that and these numbers being tossed around require a lot of other work. I remember seeing a build years go where a guy was able to get better than 2.1 HP/ci out of a 340, through a carburetor. To me that's like magic.
 
I remember seeing a build years go where a guy was able to get better than 2.1 HP/ci out of a 340
Click to expand...

More than likely....... it was noticeably better than .26hp/cfm as well.
 
PRH said:
More than likely....... it was noticeably better than .26hp/cfm as well.
Click to expand...

Couldn't tell you what the specs were but whatever heads were used would have (according to that calc) been able to flow around 350 cfm... I mean damn
 
Here’s one example.
This one only beat that formula by a few HP.
383 Mopar, 10.5CR, unported 906’s that flow 235, dual plane intake, flat tappet cam.
Made 504hp with oxygenated fuel and an electric water pump.
.26hp/cfm shows 488hp.

What could have been done to improve the power without changing the heads?
-add 3 points of compression
-modern gas ported ring pack
-vacuum pump
-dry sump
-Roller camshaft
-tunnel ram with dual carbs
-merge collectors
-q16 gas
 
PRH said:
Here’s one example.
This one only beat that formula by a few HP.
383 Mopar, 10.5CR, unported 906’s that flow 235, dual plane intake, flat tappet cam.
Made 504hp with oxygenated fuel and an electric water pump.
.26hp/cfm shows 488hp.

What could have been done to improve the power without changing the heads?
-add 3 points of compression
-modern gas ported ring pack
-vacuum pump
-dry sump
-Roller camshaft
-tunnel ram with dual carbs
-merge collectors
-q16 gas
Click to expand...


How much of a difference does that fuel make? I'd consider that not quite the same as normally aspirated (even though it is) but adding a chemical boost like nitrous to increase the VE artificially. If that's not a correct assumption fair enough.
 
Welp, nevermind. Seems oxygenated gas is just for a more complete and cleaner burn. Learned something new today! Thanks.
 
Cuda416 said:
I saw a video choosing a cam that claimed (in a general sense) if you take the flow of an intake port for a given lift, and multiply it by 0.26, that will give you the max theoretical hp for that cyl at that lift. So for magnum heads, that's 233 from the factory as far as I understand, so at that rate, each cyl should be able to support 60.5 HP, or a total of 484 HP. How far off of reality us that? I understand reality over theoretical but software can effectively predict HP based on such things so how far off is this?

Opinions?
Click to expand...
What don’t you by calculators. There are few things to bench race about when it comes to cylinder heads making power. But to break it down to simple, the KISS method would be, cfm X 2 = possible power output and only for a hot street engine. It is reasonable accurate for the basic bench race discussion of what a hot street car or mild track car can pull off.

It is not unreasonable to say a honest 300 cfm head can make 600hp and do it without going overboard on a few things that make for race type only material and fuel. You can build a 600 hp pump gas engine. I just wouldn’t try it with a small engine, like a 340 and expect it to be a grandma smooth idle smooth running delight to drive.
 
rumblefish360 said:
What don’t you by calculators. There are few things to bench race about when it comes to cylinder heads making power. But to break it down to simple, the KISS method would be, cfm X 2 = possible power output and only for a hot street engine. It is reasonable accurate for the basic bench race discussion of what a hot street car or mild track car can pull off.

It is not unreasonable to say a honest 300 cfm head can make 600hp and do it without going overboard on a few things that make for race type only material and fuel. You can build a 600 hp pump gas engine. I just wouldn’t try it with a small engine, like a 340 and expect it to be a grandma smooth idle smooth running delight to drive.
Click to expand...

Not sure what the first sentence was supposed to mean.

I believe the calculators, I'm just really surprised. I'm not an engine builder and know enough to be dangerous. I'm learning more and more all the time though and the video on choosing a cam was very eye opening. Everything was pretty basic but I'd never had it explained before as it was. So knowing this stuff is to important when it comes to making informed decisions on parts etc.

What I think it's telling me is this.

Heads left alone, will allow for some really nice numbers given the right combination. Doing other things like porting, not only increases the potential, but also lowers the "price" of entry in terms how how easy/hard it is to make power. I better breathing set of heads will allow for more power with less "magic". I'm probably messing that up and sounding like an idiot, but that's what I'm getting.

I'd love to see some pointers to papers/articles that discuss the effects of different aspects such as compression, rod/bore ratios etc on total available power etc.
 
rumblefish360 said:
What don’t you by calculators. There are few things to bench race about when it comes to cylinder heads making power. But to break it down to simple, the KISS method would be, cfm X 2 = possible power output and only for a hot street engine. It is reasonable accurate for the basic bench race discussion of what a hot street car or mild track car can pull off.

It is not unreasonable to say a honest 300 cfm head can make 600hp and do it without going overboard on a few things that make for race type only material and fuel. You can build a 600 hp pump gas engine. I just wouldn’t try it with a small engine, like a 340 and expect it to be a grandma smooth idle smooth running delight to drive.
Click to expand...

Never heard of CFMx2, that seems like a good ballpark to use.
 
I always thought this was reasonable

HP = 0.25714 × CFM × No. of Cylinders

This indicates that on a V8, the airflow/power-correlation would be:

Flow(cfm @ 28 in)

PowerPotential (hp)

100...205.7

150...308.6

200...411.4

250...514.3

300...617.1

350...720.0

400...822.8

450...925.7

500...1,028.6

“Two engines can both make 600 hp—but one accelerates, the other won’t, either on the dyno or in a car. There may be a disconnect between cylinder-head flow and port volume. Generally, at a given horsepower level, you want to see max airflow out of the smallest port possible.”
 
I get the second part of that as it seems you'd want the highest port velocity, but isn't HP by definition, the ability to accelerate, ie, work over a period of time? Higher number equal faster acceleration at a given rpm? DO I have that wrong
 
It depends on what level CR and cam duration you plan on using.

like 15:1 and 300 plus degrees might get the max hp amount out.

I’ve noticed engines with about 10:1 and 285 cams make around 1.8-1.9 hp per cfm.
 
rumblefish360 said:
I don’t buy into calculators.
Click to expand...
Fixed...

In other words, calculators are exact. The world isn’t. Nor is the input to the calculators or the person i point about what there doing. Ether by mistake or not being honest with themselves or not fully understanding the program or there build.

So there is a wide verity of possible problems. Small or large, it doesn’t matter. Though calculators aren’t a bad thing, it is just something that should not be taken as gospel. You would be amazed (maybe not, but...) at the number of people at a gathering asking me about engine power. I say I estimate 450. (Which is followed by 500 questions about the engine and insults on how stupid I am to come up with that number and I wasted my time doing ...... AKA any aspect of the build as stupid...)
They come up with exactly what I’m supposed to run.

How that is I don’t know since engine power is the only thing they have to go on. Zero consideration on gearing, type of trans, car weight and any suspension being used.

The thing here is.... human or computer calculators are all guessing until you get your *** out there and onto the track & optimize your car. Or in this case, dyno the engine. Which is also not an exact thing ether or for anything.

The dyno is a tool and that’s that. No more, no less.
Just like the computer calculators.

As I said, a good rule of thumb is cfm X 2 for hot street engines and light racing. It can be exceeded! This is not a problem. But don’t bank on a back yard hone job and slamming in the parts to reproduce the latest magazine article power house.
 
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