A twin screw is a roots, but it just twists more, almost a full turn, from one end to the other.

Ours are a 60-degree twist.

Eaton has developed one with more.....

alright, the centrifigal is like a belt driven turbo, so i suppose it spools up just as quick as a roots, but does it take the boost longer to get into the engine???

If it does, it'* not enough to notice. Plus, you can intercool them really cheap! Think diesel truck intercooler.

very big intercoolers from my experience with the ford. but yes, this has been very helpful. i schooled the guys at work today. i shut them up quick.

The difference in them comes from air movement type. The roots is a positive displacement pump. Meaning that how much air it moves per revolution is the same, ignoring small efficiency differences of how much air leaks past seals (think where the rotor tips and case meet) as speed increases and boost levels stay almost the same as revs change. There is a pysical barrier that forces the air to move. The centrifigul SC is, of course, a centrifigul pump. It doesn't push air, it spins it giving it momentum. The faster it spins, the more momentum it gives to the air, pushing harder and harder, which is why boost goes up with rpms.

C hevy..

There is no spool up in a supercharger. Being belt driven, it is moving at the rpm prescribed by the crank and it'* pulley'*. The reason you don't get boost at idle is a bypass valve. A turbo..must get spinning aka spooling up to make power, a supercharger merely closes the bypass valve and gives you the pressure instead of letting it bypass.

I wonder if the New TVS from Eaton is going ot be used on the 3800 any time soon. I'm sure it would require a different LIM or even some extensive custom work, but it'* details from Eaton sound promising.

The 3800 - sadly - is not being used in NEW GM cars, so I doubt it.

Twin-screw size for size will have a cooler charge into the engine than a root blower.

http://www.superchargersonline.com/content.asp?ID=76

Great link..