Equations..

[Edward Hernandez R]

Jim Staff, try this instead:

PV=mRT, where

P=pressure in pascals(not kPa)
V=volume in m^3(cubic meters, not liters)
m=mass of air in the volume, kg
R=287 kJ/(K * kg) for air
T=absolute temperature in K

This one does away with moles. I'll make a bold assumption that you
know what a derivative is(if not, we'll explain). Take the derivative 
of each side of that equation with respect to time and you get:

P(dV/dt)=(dm/dt)RT, where

t=time, seconds
dV/dt=volume flow rate in m^3/s. A more common unit is CFM, but you
       can perform the conversion
dm/dt=mass flow rate in kg/s. A more common unit is lbs/hr, but...
      
Rearrange to solve for dm/dt, which is what you are really after:

dm/dt=P(dV/dt)/(R*T)

Now, R is constant, you can measure P with a MAP, T with an air charge
temperature(ACT) sensor.

Throw in Volumetric Efficiency(called eta, but I can't type in greek,
so I'll call it N which looks similar) as a correction factor for
dV/dt:

dm/dt=P(N*dV/dt)/(R*T)

Now dV/dt becomes a constant(it's your engine or cylinder 
displacement), and you need to predict N(that's you asked in the first
place, huh?). That's tough to predict without any measuring equipment 
at all. You could assume a relatively safe, constant number like 70%, 
but without measuring SOMETHING, you'll never know how close that is 
or how it changes with rpm at wide open throttle(WOT).

What are you building, kart? Powerplant? Tell us and I'm sure someone 
can help you figure out a way to qualitatively determine your WOT 
volumetric efficiency. I'm thinking you could try to monitor exhaust 
gas temperature(EGT) vs rpm, which can be done without a dyno.

Hey, glad to see a high school student trying stuff like this. Life
doesn't suck after all!