OK here goes:
Engine Volumetric Flow Equation
VAF(Volume Air Flow in cu. ft/min) = (Enging RPM x engine cid) / (1728 x 2)
So in a 2.4L
VAF = (6200 x 146.458) / 3456 = 262cfm
Ideal Gas Law/Mass Air Flow
The Ideal Gas Law is a handy equation to have. It relates the air pressure, temperature, volume, and mass (ie, pounds) of air. If you know any three of these, you can calculate the fourth. The equation is written:
P(absolute pressure) V(volume) = n(related to the number of air molecules, which is an indication of the mass (or pounds) of air) R(constant number) T(absolute temp)
Lets assume that we are at sea level.
8psi of boost(psig) = 22.7psia(14.7+8)
The absolute temperature is the temperature in degrees F plus 460. This gives degrees Rankine, or deg R. If it is 80 deg F outside, the absolute temperature is 80 + 460 = 540 deg R.
n(lbs/min)= P(psia) x V(cu.ft./min) x 29 / (10.73 x T(deg R))
Lets say you are running an intercooled setup and temps in the intake manifold are 130F and you are still running 8lbs of boost:
Absolute temperature = 130 deg F + 460 = 590 deg R
Absolute pressure = 8 psig + 14.7 = 22.7 psia
n(lbs/min)= (22.7 psia x 262 cfm x 29) / (10.73 x 590 deg R) = 27.24 lbs of air per minute (ideal)
lbs air per minute actual = 27.24 x 0.85 = 23.16 lbs air/minute
Volumetric Efficiency
If life was perfect, we could fill the cylinders completely with air. If we had 17 psi boost in the intake manifold, we would open the intake valve and get 17 psi in the cylinder before the intake valve closed. Unfortunately, this doesn't usually happen. With some exhaust remaining in the cylinder and the restriction offered by the intake ports and valves the actual amount of air that flows into the cylinder is somewhat less than ideal. The amount that does flow divided by the ideal amount is called the volumetric efficiency.
To take this into account when we calculate flow into the engine, we multiply the ideal amount of air by the efficiency to get the actual amount of air:
actual air flow = ideal air flow x volumetric efficiency
Now the lower your FMIC/cooling system can cool the air by the time it hits the intake manifold, the more lbs air/min you will move. So an intercooled turbo setup vs a non-intercooled setup will vary greatly!
Compressor
The compressor is the part of the turbocharger that compresses air and pumps it into the intake manifold. Air molecules get sucked into the rapidly spinning compressor blades and get flung out to the outside edge. When this happens, the air molecules get stacked up and forced together. This increases their pressure.
It takes power to do this. This power comes from the exhaust side of the turbo, called the Turbine. Not all of the power that comes from the turbine goes into building pressure. Some of the power is used up in heating up the air. This is because we lowly humans cannot build a perfect machine. If we could, all of the power would go into building pressure. Instead, because of the design of the compressor, the air molecules get "beat up", and this results in heat. Just like rubbing your hands together will warm your hands due to the friction between your hands, the friction between the compressor and the air and between the air molecules themselves will heat up the air.
If you divide the amount of power that goes into building pressure by the total power put into the compressor, you get the efficiency of the compressor.
For example, if the compressor is 70% efficient, this means that 70% of the power put into the compressor is used in building air pressure. The other 30% of the power is used heating up the air. That is why we like high efficiency compressors; more of the power is being used on building pressure and less is used heating up the air. You want to be in the 65% and higher efficiency range.
How to read a compression map(that I posted above)
Figure out the pounds of air that you are moving through the engine. We are passing 29.77 lbs/min of air, at inlet conditions of -0.5 psig and 70 deg F. Now correct that flow to the standard temperature and pressure.
Corrected flow = (actual flow x (Tin/545)0.5) / (Pin/13.949)
The standard temperature is 545 deg R, or 545 - 460 = 85 deg F.
o we are correcting the flow from 70 deg F and -0.5 psig to 85 deg F and -0.75 psig.
Tin = 70 + 460 = 530 deg R
Pin = -0.5 + 14.7 = 14.2 psia
Corrected flow = (23.16 x (530/545)^0.5) / (14.2/13.949) = 22.45 lb/min
Now for Mitsu maps, they use CFM, Garret uses lb/min. Every 10 lb/min is equal to 144.72 cfm. So:
CFM = (22.45 lb/min / 10) * 144.72 cfm = 324.9 cfm
So we mark that point on the bottom of the graph, and draw a straight line upward from that point.
The next step is to figure out the compression ratio, using absolute pressures. Using our example, we had 8 psi boost in the intake manifold. Let's suppose the pressure drop from the turbo outlet to the manifold is 3 psi; so the actual compressor outlet pressure is 3+8=11 psig. The air pressure is 0 psig, but since the turbo is sucking air to itself the pressure at the inlet is lower than that. Let's say it is -0.5 psig at the inlet. Then the compression ratio, Pout/Pin is :
Pout/Pin = (11 + 14.7) / (-0.5 + 14.7) = 1.81
So then we find about where 1.81 is on the left side of the graph and draw a line horizontally from that point. Where the two lines meet is where the turbo will operate.
SO using my 1337 skills in MS Paint:
Here the efficiency range for those turbos on the 2.4L:
http://img299.imageshack.us/img299/8655/14b4mj.th.jpg
14b = 72% @ 400cfm
http://img364.imageshack.us/img364/4...l16g0xl.th.jpg
Small 16g = 76% @ 495cfm
http://img364.imageshack.us/img364/2199/b16g3dg.th.jpg
Big 16g = Borderline 71% @ 475cfm
http://img364.imageshack.us/img364/5963/e316g9ku.th.jpg
Evo3 16g = 74% @ 540cfm
http://img364.imageshack.us/img364/3671/18g7zj.th.jpg
18g = Upper end of 77% @ 540cfm
Now these calculations are all at 8psiag at a 6200RPM redline. They all are pretty efficient for our cars. Technically you want the turbo that is most efficient for our engines. at all RPMs. At redline, the 18g proves most efficient. But that also comes with a higher spool rate which I am not going to calculate simply because I do not know how.