Calculating maximum hp

What is the equation to calculate an engines maximum theoretical power asuming you know the displacement, air flow and volumetric efficiency?

Originally posted by Socrates
What is the equation to calculate an engines maximum theoretical power asuming you know the displacement, air flow and volumetric efficiency?

How would you know the VE? There are a few engine simulation programs that could do what you ask. Remember, GIGO applies.


Here's a recent post that might help:

Originally posted by AdioSS

I think I was asking for a way to figure out the max potential horsepower just from looking at how much air the heads can flow.





Courtesy of David Vizard and Superflow:

Assume everything like exhaust is optimum, which is a challenge:

You need, for a 10:1 350 cube SBC:

1) head flow at full intake lift value at 25 in H2O. If you have 28 in. H2O numbers, multiply 28 in numbers by .89286.

Multiply that number by 2.05 for hydraulic roller, or 2.1 for a solid roller.

If you have a 400, multiply again by 1.1 or .95 for a 327 or .9 for a 302.

For 11:1 multiply by 1.07

Example 1: 230 cfm (at 28 in H2O) x .89286 x 2.1 x 1.07= 461 hp at the flywheel.

Example 2: 290 cfm x .89286 x 2.05 x 1.05 (my guess for a 383) = 557 hp at the flywheel.

Remember, this is with everything spot on.

Originally posted by OldSStroker
How would you know the VE? There are a few engine simulation programs that could do what you ask. Remember, GIGO applies.


Here's a recent post that might help:



Courtesy of David Vizard and Superflow:

Assume everything like exhaust is optimum, which is a challenge:

You need, for a 10:1 350 cube SBC:

1) head flow at full intake lift value at 25 in H2O. If you have 28 in. H2O numbers, multiply 28 in numbers by .89286.

Multiply that number by 2.05 for hydraulic roller, or 2.1 for a solid roller.

If you have a 400, multiply again by 1.1 or .95 for a 327 or .9 for a 302.

For 11:1 multiply by 1.07

Example 1: 230 cfm (at 28 in H2O) x .89286 x 2.1 x 1.07= 461 hp at the flywheel.

Example 2: 290 cfm x .89286 x 2.05 x 1.05 (my guess for a 383) = 557 hp at the flywheel.

Remember, this is with everything spot on.

I wouldn't expect over 2 hp per cfm like the wizard says unless you have a pretty nice short block, and lots of compression. But it's still close. I'd say something more in the 1.90-1.95 range would be closer to reality for the average street motor.

Later
Chuck

Estimated hp based on CFM

HP = .2575 x CFM (@ 28" or water) x number of cylinders

Originally posted by OldSStroker
How would you know the VE? There are a few engine simulation programs that could do what you ask. Remember, GIGO applies.

I’m just assuming VE is 100% simply to get the maximum theoretical hp even though it’s actually quite lower in real life.

Originally posted by OldSStroker
Assume everything like exhaust is optimum, which is a challenge:

You need, for a 10:1 350 cube SBC:

1) head flow at full intake lift value at 25 in H2O. If you have 28 in. H2O numbers, multiply 28 in numbers by .89286.

What do the 25 and 28 denote?

Originally posted by OldSStroker
Multiply that number by 2.05 for hydraulic roller, or 2.1 for a solid roller.

If you have a 400, multiply again by 1.1 or .95 for a 327 or .9 for a 302.

What do the various numbers for those displacements mean? I though an engines power was only related to your head flow and not displacent, assuming RPM was not a factor of course.

Do you have a list of more constants for other displacement?


Originally posted by OldSStroker
For 11:1 multiply by 1.07

So for the 10:1 the constant is 1? Do you know more constants for other ratios?

Originally posted by OldSStroker
Remember, this is with everything spot on.

Only head flow has to be accurate?

Thanks a lot for your help I found this very useful :bow:

Originally posted by Stephen 87 IROC
Estimated hp based on CFM

HP = .2575 x CFM (@ 28" or water) x number of cylinders

HP = 0.2575 x 200 x 8 = 412 hp

I'm guessing this result is a very optimistic, assuming you have a perfect exhaust typically how close is it to the real world :confused:

An engine is just a vacuum pump. When the piston moves down pulling in the air/fuel mixture, the restriction is still the heads/valves. Theoretically the same heads, cam, valves, intake, carb, compression ratio, etc on a 350 will produce the same amount of HP as a 400. The difference is the amount of torque that the engine will produce (which is what a dyno measures) and where in the rpm range the power is produced.

To make more HP you need to burn more air/fuel. That's why power adders such as turbo's, blowers or NOS work the way they do. They all do the same thing by increasing the amount of air that gets put into the cylinders. By increasing the amount of air you can also increase the amount of fuel which will produce more power.

NA engines need to rely on the engine's ability to draw in that air/fuel mixture from head flow and cam profiles.

Well designed NA setups exceed 100% VE, though within a relatively narrow rev range.

Rich Krause