[Tom Vaught]

JSPONT.

Boost People have for years tried to match the low speed drivability of a small roots supercharger vs a larger turbo.

The small roots supercharger (example) 90 cubic inch per revolution Eaton Supercharger (used on the 3.8L Buicks and Fords) vs the Turbocharged early Ford 2.3L engines. 2.3L stuff gave you a bit more hp on the top end but drove and transitioned poorly at low speeds.
Turbo and Belt SC Guys have fought that OEM war for years trying to sell their parts.

So the VW Compound SC/Turbo deal was one of the first successful STAGED sequential boost systems. Roots at low speeds and Turbo at higher speeds. (They used a A/C type Clutch to turn off the Supercharger at higher speeds when the Turbo was doing its thing). Not compounded, STAGED.

I drove one of the 1st Staged VW systems in the USA (Borg Warner was doing the Turbo side of the design and the Borg Warner Head Engineer brought me the car (for my evaluation). It was a nice system. Only draw back was the A/C type clutch could not energize (at speed) to bring that SC device back on line without a noticeable dip in the power. You get the "clutch slip" right and the parts wore out quickly. Bad for warranty.

But the VW was impressive to drive except for that issue.
People (including Ford) tried Magnetic Particle Clutches vs the A/C type clutch with limited success, MP Clutch did not wear out but the unit was large and hard to package in the typical vehicle.

Tom V.