[rammertide07]

Searched another way and found some stuff. I like the way one guy explained it:

"Basically, the objective of Turbochargers and Superchargers are the same: To force a larger amount of air into the combustion chamber, adding oxygen to the combustion process, increasing the force of the explosion, resulting in a stronger power output.

The basic difference is the way they are themselves driven, more than what they actually do to the engine.

Basic difference: Supers are driven by the engine power - Turbos are driven by the exhaust pressure, but in general, the idea is exactly the same.

Superchargers (blowers) are mechanical, and use a belt from the crankshaft to the blower axle to spin up and compress the air through the intake. A deficit of this way of doing things is that the force it takes to drive the supercharge is taken from the engine, reducing power output slightly compared to a turbo at the same pressure rate. A benefit however, is that the supercharger adds power in a very linear way. The more revs on the engine, the more revs on the blower, hence more power increase. This makes the power very smooth and easy to control.

Turbochargers use the pressure of the exhaust gasses to spin up a turbine. The benefit of this is that you have no mechanical strain on the engine, and get full effect from the added pressure all the way to the driveshaft. Deficit is that it relies on the pressure of the exhaust gasses to build, causing what is know as "turbo-lag", where almost no increase is found at low revs, but once the pressure is built up, the power increase is very sudden and can be hard to control. Another benefit is that the pressure can be a whole lot higher from a turbo than from a supercharger, easily higher than what the engine can handle, which is why turbo systems often include a valve - or "wastegate" - to allow excess pressure to bypass the turbo. This valve is the cause of the little whistling sound that turbos make when taken to the limits. Turbos are also known to "tick" after the engine has been shut off. This is the turbine spinning down.

Want power? Go turbo! Wan't torque and controllability? Go supercharger! Want quick and cheap fun? F*ck air - go nitrous!"

So guess thats why the duramax had the supercharger feeding the turbos. Instant pressure on the "exhaust side" of the turbo to spin them up faster and the turbos are capable of producing more boost...and the supercharger can keep them spun up even after engine rpms drop. Except I dont think boat engine rpms drop. I would see it as a benneficial set-up in something with a transmission though.