PSI Screw

How much cfm does a PSI D rotor charger move? Is there a chart somewhere?

 

Here is info I saved from an old post that might help:

PSI "D" is 422 cu.in.per/rev or 6.752 liters per/rev

PSI "C" is 476 cu.in. per/rev or 7.616 liters per/rev

Whipple R980 & A980 is 612.5 cu.in. per/rev or 9.8 liters per/rev

So if you look at SFI max overdrive based on safety and then parity based on swept volume per/rev in 1996 this is how NHRA wrote there rules,

Top Alcohol Dragster,

PSI "D" 422 cu.in. x 2.15 or 115% = 907.3

Whipple 601 cu.in. x 1.52 or 52% = 913 (.6% advantage in swept volume as it was wrote however based on the math 9.8 liters per/rev it should have read 612.5 cu.in. x 1.52 or 52% = 931 (2.6% advantage in swept volume)

Top Alcohol F/C,

PSI "D" 422 cu.in. x 2.25 or 125% = 949.6

Whipple 601 cu.in x 1.60 or 60% = 961.6 (1.2% advantage in swept volume however just as before based on the math 9.8 liters or 612.5 x 1.60 = 980 (3.2% advantage in swept volume)

Considering the fact that the swept volume per/rev is the only legitimate way to establish a fair and level playing field it is then up to the manufacture to design a supercharger that best meets the applications requirements for safe operation at a required operating overdrive limit per SFI regulations after that has been established the supercharger with the highest adiabatic and volumetric efficiency and the least parasitic loss at high20pressure with a linear airflow curve will then allow the engine to create the highest net torque/horsepower curve based on superior air delivery.

There has been a few questions about how a PSI "C" and "D" compare so here it is in overdrive a "D" at 125% would be approximately the same as a "C" at 104% so just over 10% 2.25/2.04 = 1.102 - 1 = 10.2%

The last question that comes to mind is how to tell the difference between a "D" and a "C" measure the female or driven rotor lobe thickness, there are small variation based on application and date of manufacture or customers specific needs but on average a "C" will measure .483-.485 a "D" will measure .594-.596 both blowers have a open port in the housing between the front shaft/bearing supports.
I hope this sheds some light on the questions that have been asked.

Reprint from old post I saved.I think it was from Roger.