318 supercharger
Is it true (so I've heard) that roots are less effective then the centrifugal kinds?
Depends on who built the Roots and there internal design.
If you go to the basic roots, the issue is the design of the rotors and how well they keep and force air into the engine. There now coming with more and more of a twist on the rotors and teflon tipped on the rotor ends so theres less clearance and more air being trapped and forced into the engine.
Heat is another issue with a roots blower. A few years back, a intercooler was designed for the roots blower. It gets saandwiched between the blower and intake. Typically, this adds 3 or 4 inchs of height to an allready high/tall set up. This is not to atractive to some people as vision is an issue without the added height and may be in violation of some laws.
The bennifit of a roots Supercharger is massive.... and I mean massive torque NOW andytime the pedal is pushed and will make superior HP up top.
These two draw backs can be over come and the two advantages can be great, if built right, otherwise, someone with a well designed turbo or centrifical blower will make more power and beat you on the contest.
Some of the more expensive roots styled superchargers from Whipple, for example are among the best units you can use and are very very efficent. But be prepared to spend.