Originally Posted by James B.

Spoolin - Positive displacement and twin screw compressors spin with very little mechanical losses to friction. Under vacuum there's almost no parasitic draw on these types of compressors. Air moving against a surface creates friction. The faster that air moves the more friction and heat are created. Overcoming this friction transforms mechanical energy into heat. The heat is transferred to the air. This is why efficiency falls off at higher RPM - more energy becomes heat. In a roots or screw supercharger you have two counter rotating rotors. In a roots blower they spin the same speed, in a twin screw compressor the second rotor is geared up to spin faster. The mass of the rotors in both designs creates a lot of inertial load on the engine. In first gear, for example, when the engine is revving up fast, inertia of those rotors has to be overcome with input torque. It takes a lot of energy to accellerate a few pounds of aluminum from 1500 RPM to 16,000 RPM! Then, when the transmission shifts, you have all the inertial energy trying to overspin the crank pulley since the engine loses RPM much faster than the blower. That can cause the belt to jump off the pullies and/or even break the belt tensioner. The larger displacement compressors reduce inertial forces even though the rotors are more massive. There's a lot less accelleration of those rotors due to the slower rotation to achieve the same boost.

The belt around the 2.625" pulley on my W140AX is not slipping, amazingly. If I were running the larger W200AX compressor at the same boost levels I am getting from the 140, the puley would be much larger giving the belt more grip and more leverage on turning the rotors. The 6-rib serpentine system would work fine with that. My biggest problem is with engine decelleration adn the compressor overspinning the crank. It shifts all the belt slack to the driver side of the crank pulley and pulls the tension so tight it maxes out. This happens during shifts and after burnouts when the tires grab. (Any time the engine RPM rapidly decreases)

Originally Posted by James B.

Funny you mention this, I've thought about doing something very similar. One of these days I am going to try to fabricate a crank pulley that has a roller clutch or a sprag from an automatic transmission in it. It will serve as a mechanical diode.
I think it would work well.

Originally Posted by Stoichiometric

The bigger superchargers definetly take more engine power to turn, you get into 8 rib, 10 rib then cogged belts to drive them. The payoff from the larger compressors must be worth the increased power they consume, they make more HP.

I was a little curious what it would take to make 1K RWHP with a supercharger. There was a thread on the Corvetteforum that had a 408 with the KB 2.8 making 8xxRWHP. That was on ~21lbs of boost (unsure of pulley size), manual trans I think. It seemed that the set-up was pretty well maxed out, so I would assume a bigger compressor is needed to make more power. I can't wait to see some results from the trucks around this site!

James, do you have any belt slip or feel the need to upgrade the drive? If you were to run the 200ci compressor, what belt would you use?