I hear a lot from the turbo guys that a blower is ineficent due to parasetic drag, but how ineficent is a modern centrifugal blower? Has to better than like a roots or some thing.

 

I have a book (yeah I know, paper pages and all! ) at home with efficiency graphs for various blowers; roots are pigs. What does a Top Fuel motor take, 500 hp to turn the blower?
The other thing about blowers is that they are rpm dependent, so unless you overdrive the crap out of them you have to build rpm to see boost.
Turbos can use housings and impellers to determine when they spool, at the expense of exhaust flow.
There is no such thing as a free lunch, but I think the turbo is more efficient, at the expense of more complex piping.
If you want a power adder that totally eliminates loss use nitrous.

The old F1 and current CART cars use turbos, and they are all about efficiency and minimizing parasitic losses.

Surf around the Banks site, they have some interesting comparisons..

 

Well there is parasitic drag and there is adiabatic efficiency. Turbos have parasitic loss from exhaust back pressure...somewhere around 2:1 backpressure to boost ratio. Not sure exactly how much this equates in hp loss, but it is generally accepted to be less than the parasitic loss from a supercharger.

Adiabatic efficiency wise turbos and centrifugal superchargers are almost the same, with turbos getting the nod because you can get a custom setup for your engine that is most efficient where you want it. Centrifugal superchargers are basicly a crank driven turbo. Roots style superchargers are not very efficient compared to the others but have some advantages being a positive displacement supercharger (instant boost). I do hear that whipple style superchargers are the more efficient than the rest though.

Adiabatic efficiency is how much heat the compressor adds to the air from compressing it btw. 100% would have the only heat added from compression (ideal gas law), Roots=50%-60%, Centri/Turbo 70%-75%, Whipple ~80%.