You're right, the Roots type would be simply an economic choice, but because it's still useful enough to be considered at all, even as just the "economy blower", I would argue that it's not obsolete. If you really want to get into the semantics of it, Dictionary.com defines obsolete as "no longer in use", and because it is still used, for whatever reason, that would contradict this definition.

 

Most top fuel dragsters still use roots. Maybe for the same reason as new car makers: because they are the simplest superchargers with the least number of moving parts.

Why would you choose a centrifugal over a twin screw? If you have serious tire hooking problems off the line, it could be used like a turbo (launch off boost... then boost kicks in after you're moving) Or if you want to run an *** load of pressure. Or if you want to save some highway cruisin MPGs, or maybe your rpms never drop below 3 or 4k

Why would you choose a twin screw? Max boost output at idle, continues up through powerband, only drops 1 or 2 psi at the top end

Why would you choose a roots? Simplest design, least amount of crap to break

 

from what i understand twin screws work much more simple that roots, pushing the air straight through instead of out and around...

 

Exactly, and thats one reason why they are more efficient that roots type units.
Most all the competitive top fuel dragsters run set back screw blowers.
I'm still waiting for someone to name a current production car using a roots blower.

 

there are quite a few production cars that run roots blowers, grand prix, cobalt, etc... all the eatons. Cobra/Lightning....

 

Did anyone hear about the volkswagon twincharger? Supposedly its a 1.8 with a supercharger and a turbo. I actually want to learn more, even though its a volkswagon.

 

thats interesting, i wanna know how that works. I always thought one way or another that setup would try to fight itself...

 

http://www.superchargersonline.com/content.asp?id=22
http://www.strokerengine.com/Supertech.html

Two websites stating top fuel dragsters use roots, one stating it's because mostly rules are against screw type, one stating simplicity of design

Not saying twin screws arent used, just saying most Top fuel and nitro methane drags are known for huge roots blowers

Also, saleen still makes roots blowers

 

And not really, the supercharger would make the boost all the way through the rpm range, draining maybe 10-15 horses from the crank, and the turbo (which drains barely any hp) would probably spool up later... it'd be kinda like a TT design... but with absolutely no turbo lag.

The turbo or super, whichever was second, might have to be built bigger/stronger because it's already working with pre-compressed air, if they're working in series, but if they're working in parallel (i dont know how that'd work) they wouldnt have an effect on each other

 

well, saying they were in line, the supercharger would start boosting the engine, then the turbo, if the blower was pushing more air than the turbo, the turbo is useless. If the turbo is pushign more air than the blower, the blower is just in the way...