No, turbochargers are superchargers. The name is a contraction of "turbo-supercharger". The only functional difference is their power source. In fact, if you look at a turbo and a Vortech side-by-side, the similarities are obvious.

It looks like you're confusing mounting conventions with device type. While the stereotypical Roots blower is bolted to the top of a hemi motor, that's not what distinguishes a positive displacement supercharger from other types. Positive displacement blowers move a fixed amount of air per RPM, because the internal mechanism is sealed, preventing air from escaping. They have a fixed displacement. Centrifugal types use centrifugal force to build pressure, and air can leak back out at low RPM. That means they're not linear like positive displacement blowers; they have different efficiencies at different RPMs.

http://www.grapeaperacing.com/GrapeA...supertypes.cfm