That's a simple one - Roots are cheaper to product and the OEM's like cheap and reliable. The complex curves of the male and female twinscrew rotors make it much more expensive to produce. But when a Cobra wants a hefty upgrade, they switch to a KB or Whipple twinscrew, usually bigger, but for the efficiency as well. Twinscrews actually are compressors where Roots (including the newest Eaton TVS) is only an air mover. That gives the twinscrew a leg up on the efficiency curve which translates to less heat at a given boost level.
Jim
__________________ Don't bring a knife to a gunfight. 
Half-Assed = Half Fast. |