"I've always wondered, has anyone ever built an engine that was actually set up like that? I imagine it would take a lot of custom plumbing. " Actually its done all the time. Volvo's 32,42,43,&44 series marine engines all have an electronically controlled (Roots) s. c. While the first 3 look at rpm as a controlling parameter, the 44 is ecm controlled, so as a cold weather aid as well as a load sensing ability can also control blower operation. The first 3 can all use a helm switch to bypass the rpm signal to eliminate the s. c, for trolling or whatever, but you would not want run the s. c up high, as speeds are 3-4x crankshaft speed. All are plumbed the same- basically you have 2 outlets from the aircleaner. The first goes thru a flapper valve, directly to the turbo then the a. c. -you know the rest. The second goes to the supercharger, then to the turbo, on the back side of the flapper, so when there is pressure there, the flapper is pressed closed, thus causing all the air to be drawn into the s. c. Simple! All this was really done to offer high torque from idle on up, When the blower goes off around 2500, the turbo comes on, and you have a sweet band thruout. ... . Now somewhere around here I just happen to have a s. c and all kinds of hood clearance. . more on that later!!