Quote:
Originally Posted by GuidoK
you can make calculations, but at least the graphs you posted dont add up, not by a long shot.
Or at least if its a compare between the same superchargers.
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Which graphs are you looking at?
Quote:
Originally Posted by GuidoK
I mean at 6600rpm they make the same amount of boost.
At 6600rpm the adiabatic efficiency is 16% difference (a lot, but say its correct; it's in the graph)
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At 6600 rpm, the twin screw's adiabatic efficiency is 59.5% and the centrifugal is 70.5%
Quote:
Originally Posted by GuidoK
...the overall efficiency (I calculate the twinscrew) is 60%, and the wheel hp difference is 50hp.
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I used 9.0 CR for the twin screw. At 6600 rpm:
@11.5 CR for the centrifugal, there is a 10.3% difference in horsepower
@10.7 CR for the centrifugal, there is a 7.5% difference in horsepower
You're missing the effect of the change in CR. I multiplied the base power by the change in CR using the rule of thumb of 4% per point in CR. The 2.5 point difference equates to 10% more power at 11.5 CR. This was part of the exercise... to see whether low compression / high boost twin screw trumped high compression / high boost centrifugal... and the differences in power consumed, discharge temp, etc.
One thing to note is that the numbers are only accurate at wide open throttle. At part throttle, efficiency is difficult to estimate and would probably require modeling software.
Quote:
Originally Posted by GuidoK
That means that at that point the twinscrew supercharger is consuming 125WHP/150crank (60/16*50) of power  |
No. I have a separate graph of horsepower consumed. At 6600 rpm, the twin screw is consuming 17.6 hp, while the centrifugal is consuming 16.2 hp.
Quote:
Originally Posted by GuidoK
You understand that there must be something wrong there dont you? 
superchargers consume power, for sure, but not thàt much |
There were generalizations made for the behavior of the different types of superchargers. However, most of the rest of it... other than using the rule of thumb for CR; and (wheel horsepower) = (stock NA wheel power)(CR change)(PR) - (horsepower consumed by the supercharger)... is pretty accurate. I am more than happy to share the formulas I used so you can draw your own conclusions.