Reply to "twin turbos"

The 150 hp gain from 5-7 psi may be optimistic, depending on what else you do to your engine. Rule of Thumb is, 14psi boost will effectively double the horsepower one gets from a given engine. So if the engine is properly built for supercharging, it may only put out 200 horses without the blower, so theoretically a 7psi boost on that motor will give another 100 horses.With a supercharger, I find it helps to consider that part of the engine's compression ratio resides in the blower boost. Many supercharged engines run 8:1 or even 6:1 mechanical compression, getting the rest from their little wind machines. Conversly, running 10:1 c.r with blower for instance is usually a recipe for a 'grenade engine,' unless extraordinary ($) mechanical things are done to the engine, such as aftermarket rods, forged pistons with the ring pack positioned low for a thicker piston crown, short-overlap cam, special head gaskets etc.