[Tom Vaught]

Well Travis, my little excel spreadsheet (compliments of Dave Austin and verified with the math & physics formulas) says that at 40 psi, 85 degree inlet air, 74% compressor efficiency, 12% parasitic losses, and the supercharger actually moving 240 lbs of air per minute (2400 horsepower) would suck up 505 horsepower.

I would say that we are in agreement on your post.

Tom Vaught

Bruce, that Rule of Thumb "10 hp of drive for every 100 hp added" or "One Hp to move One Pound of Air Mass and 1 lb air mass makes 10 hp" " only works for a pressure ratio of about 2 (15 psi boost) At 20 psi of boost you are talking around 120 hp to move 100 lbs of air mass. At 240 lbs/min you would be talking 300 HP. Raise the boost to 25 psi and you are around 150 hp for 100 lbs air mass. 350 hp to move that 240 lbs of air mass. You get the idea.

[Travis Q]

To add a little more to the discussion:

Something else to consider is that a pump, ANY pump, be it fuel, oil, or air, takes a given amount of horsepower to move a given amount of fluid at a given flow rate.

ACCELERATING this pump from a low flow rate to a higher flow rate takes a great deal more power than operating it at steady state. The faster you wish accelerate this pump, the more power it takes.

This is critically important when speaking about superchargers on race cars, because, unfortunately, they don't operate at steady state for very long. The faster we wish to accelerate the engine, the faster the blower must accelerate as well (it's tied to the crank snout, after all). And, since the power requirement to accelerate the blower increases non-linearly, that blower better be able to keep up when it's called upon.