electric superchargers, electric superchargers Options

[sanman]

Has any one seen these?
Not that i want one but I figered club 914 should have a thread
IMOA I dont think a FAN can make boost or am I wrong
whats your opinion?

[lapuwali]

The one actually marketed as the Electric Supercharger is basically worthless. Nowhere near enough power at the fan to provide any real boost. Something like 5 years ago, when they first appeared, several 911 types in the Bay Area got together, managed to talk the shop out of one for eval purposes, put it on the car and the car on the dyno, and came up with no increase. 2-3hp, maybe, on a 200hp engine, which put it down in the measurement error category.

The big conceptual problem with these devices is the power loss required to drive them. An efficient direct belt-driven supercharger takes 4-5hp to drive it at 8-10psi. 5hp is 3.7kW, or 308 amps @ 12 volts. This is Otmar class electrics. Assuming you could somehow find a 300 amp alternator, you'd need to drive it, and you'd see a power loss on the order of 50%, so it would take 10hp from the engine to drive a 300 amp alternator. Now, you could just draw off a battery for short periods and get enough power to drive a pretty hefty electric motor to drive a blower, but it would really only be for short burts, like one 1/4 mile run or something, with a long period waiting for a normal-size alternator to recharge the battery.