Originally posted by NSXTC:
You guys are both right about the efficiency of the two basic different types of SC designs. However, here is the piece of the puzzle that is missing from this discussion which I think will resolve the paradox of why one SC system makes more power than the other. The CT SC is indeed a twin-screw type blower, which is in general more efficient than a centrifugal SC.
The rub, however is this: the particular Lysholm roots-type unit that CT uses just happens to reach it’s max efficiency at around 8.5 to 9 PSI with the NSX motor. What starts to happen at this boost level, with this particular blower is that the heat buildup is so great as to really start to take away from your peak dyno numbers. What the CT SC was designed to do from the get-go was to produce low-end grunt, not just peak dyno numbers.
Are you sure about the "screw" type versus the "roots" type? I know that the M uses a "roots" type of blower. The difference is in the rotor design. The screw develops its boost in the supercharger itself as it compresses the air then feeds it to the intake manifold. The roots sweeps air into the manifold where it develops the boost in the manifold. The heat is generated in the roots from air trying to retrace itself back into the supercharger. Also, some roots have teflon ends where the rotors try to seal the unit against the casing. This rubbing causes heat. The screw type's tolerances and rotor design enables compression and stops air from retracing back without touching (or minimal touching if any). With the twist in the rotor, it is able to compress the air in the supercharger and then send it to the manifold. This is what makes the screw type different and more efficient. The centrifugal design is awesome if you can keep the speed of the compressor wheel within its efficiency window. Unlike a turbo where you can tune the speed of the compressor wheel independent of the engine speed, the centrifugal design supercharger is dependent on the RPMs your engine puts out--too slow.... the air bleeds backwards--too fast the air get into turbulence due to the sound barrier build-up on the compressor fins. That is why the centrifugal supercharger has a PEAK efficiency window. Also, that is why properly turned turbos favored by many. Whew!!! That was confusing!!! Not bad from a Behavioral Scientist!!!
Regards,
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Kenji Ligon
91 Red CTSC NSX
[This message has been edited by Attitude Adjuster (edited 04 January 2002).]