I was interested in knowing how much HP is lost between the Engine and RW.
And how to retain as much HP as possible.

I recently called Speedcraft. They told me if I install the turbo and run it a 6 psi w/o headgasket and
racing fuel. It would produce 280hp at the RW. To understand what this really means, I would have to know
approx. what the HP is at the RW as stock(My car is stock.)

 

Stock RWHP is ~200 plus/minus 5hp.

 

RW?..I assume you mean rear wheel horsepower (rwhp). Rwhp is the amount of horsepower the car is actually making at the WHEELS! All engines make a certain amount of horsepower. The S2000's engine for example, is rated at 240hp. However, since NO CAR is perfect in its power delivery the amount at the wheels (front, rear or all four) is less than the quoted engine power. Drivetrain loss is what many people call this loss of horsepower. The average loss from the engine to the wheel is about 15%. However, this percentage varies from car to car and engine to engine. NOTE: AWD autos lose more power since power delivery is doubled. So 280 rwhp is about 329hp (assuming the 15% loss value) at the flywheel or engine (sorry I won't introduce new terms).