I'm wondering that myself Marty. When the intercooler is added the system curve will shift even farther to the right.

I have some data from an old magazine test in which Vortech added an intercooler and picked up HP without increasing compressor RPM, even though the boost went down slightly and even though we know the resistance to air flow had to be higher. I worked this out in another thread a while back. The intercooler drops the pressure in the intake manifold, because as temperature is reduced, pressure X volume must go down (Boyle's Law). But since the engine, a positive displacement pump, controls the volume, pressure must go down.

This is seen by the compressor as a reduction in total system resistance, and at the lower compressor discharge pressure, the compressor flows more air. Since the intercooler adds power, the compressor must be moving more air.

This means that both the standard intercooler curve and the improved intercooler curve will shift over to the right. In that magazine article HP increased from 449 HP to 481 HP so let's say the compressor delivered about 7% more air. If we apply that number to the 1100 CFM of the standard Vortech system with the V-7 YS compressor, we would have a new operating point of about 1175 CFM @ 9.7 psi, (the green curve).

That's a nice gain over the non-intercooled setup, but the main reason for intercooling is of course to get the temperature down so you don't have detonation.

The big revelation is how the sins of higher resistance are covered up by the cooling effect of the intercooler. That's why we never think about it; the overall result is good.

So if turning on the water in the standard intercooler setup got us from 1040 CFM to 1175 CFM, we can assume that turning on the water in the lower resistance intercooler setup will add a similar % in air flow. But the starting point of the improved setup is much better; 1120 CFM.

(1175 CFM/1040 CFM) = ~13 %

1120 CFM X 1.13 = 1265 CFM

The new operating point will be about 1265 CFM @ 9.1 psi (compressor discharge pressure). For the first time we have strayed over the 72% efficiency line on the compressor map (yellow curve). We had also better hope that our intercooler does work better in the improved setup because we are asking it to cool 7.7% more air (1265 CFM/1175 CFM) than the standard setup.

We are starting to get into an area where a larger compressor might be helpful. We are also starting to approach ridiculous HP levels. This compressor spinning at 40,000 RPM made 780 HP @ 10 psi in the Car Craft test. By going to lower system resistance and intercooling we are predicting 890 HP. I can't see that living for long in the marine environment. I think that I would be more inclined to run the compressor at 35,000 RPM (5000 engine RPM)and make 765 HP @ 6.6 psi compressor discharge pressure. Intake manifold boost with the intercooler and lower resistance components might only be 4 psi but who cares, it's air flow that counts.

This operating point would be right on the 72% efficiency line. That's not bad, but a larger compressor running just inside the 74% island would be even better. The only caution is that a larger compressor may not have as much midrange. At 3500 engine RPM the compressor is spinning at 25,000 RPM, and if you suddenly opened the throttles the compressor discharge pressure would be just under 3 psi; intake manifold pressure only 2 psi. This should be enough since the compressor/system would be handling 50 lb/min of air, enough to instantly apply 500 HP.