I put this equation into tunerpro awhile ago and it worked somewhat, but it's not perfect. Here's where the equation can be found, but there's no explanation of what 792001.6 is. Does atmospheric pressure need to be 14.7 or is it actual atmospheric pressure (about 12.1psi where I live), and how do I make this work with forced induction?

A * C * (X * .01) * B * R / 792001.6

Where A is atmospheric pressure, B is engine dispalcement, C is static compression ratio, R is RPM and X is VE.

 

Maybe manifold pressure be substituted in for A to make it work with forced induction?

 

Seem to get reasonable estimates when I put manifold pressure in for A, but only above atmospheric. I need a way to limit the minimum for A to atmospheric pressure, is there a way to do this with a formula?

 

For a rough estimate I use the BSFC, injector flow rate, number of injectors, and the injector duty cycle. Gets close to flywheel HP.

RBob.

 

I'm looking for something dynamic though. I could throw a guess of .5 BSFC at it, but how can I calculate actual BSFC without horsepower? I think the above formula is the way to go. Just need to find a good way to tweak it for forced induction.

 

I used 14.7, live RPM and airflow data and at idle I get 5-6 HP and the VE calculates out to .02-.04 sound right?

 

VE should be higher. You can calc it using this-

M * .132 / (491.67 / (A + 459.67) * .0808) / (E * R / 3456) * 100

Where A is IAT, E is engine displacement, M is MAF (in g/sec) and R is RPM.