Horsepower Per CI vs VE

[PFM]

Hello all,

I am trying to find a correlation between Horsepower per cubic inch and Volumetric Efficiency. I read that some prostock engines are making better than 2.5 HP per cubic inch at 9000 plus RPM. Is there a path back to VE from this as a start?

It's the math problem again :-(

PFM

 

[sreid]

This may not be what you are looking for but this link has the old PLANK formula about 3/4 down the page.

http://www.loeff.d

 

[schmidtj86]

I think you would need the HP, Displacement, BSFC, and the Air/Fuel ratio to get VE. You know HP and Displacement. The BSFC and AF will be difficult to obtain, as they may be top secret, or unknown.

 

[1Bluegrass]

Using one of the software dyno programs will give you a good grounding on all this by setting up an engine, looking at the results including efficiency, then making changes to see their results.
I run a 351 cu/in engine on alky and get about 1.5 hp per at 6800 rpm through a 4 barrel and long tube stepped open headers.
This is far from pro stock performance but I am limited to rules and know there is a great deal more power there even without increasing displacment.
It would take a cam change, more airflow/rpm and compression.

 

[sreid]

Take a look at this website.

http://www.epi-eng.com/index.html

 

[EngJW]

There is no correlation, other than better VE should give you more power. Power per cubic inch (power per liter is also used) is just one of several easy ways to compare different engines. All you need to know is the peak power and the displacement. You could say that a higher number represents a more efficient use of the package. You are not relying on boring and stroking alone to get more power.

It says nothing about the means used to get that power. It is just a catch-all term that includes such things as VE, compression ratio, combustion efficiency, friction, and rpm. It also does not consider if the engine is supercharged or not, unless you know that or it is stated. And again, it removes the bigger is better syndrome from the equation.

As far as engine speed goes, you could have two almost identical engines and of the same displacement. If one of those engines can be pushed to a higher rpm, it would have a higher hp per cubic inch.

Bmep is a better term because it eliminates engine speed from the comparison.