Electric Superchargers - a scam?

[oliverg]

Hi guys - not knowing much (enough) about cars, I wanted to find out if anyone knew anything about these "electric" superchargers that are selling on ebay:

http://cgi.ebay.com/ebaymotors/Porsche-911-944-928-Boxster-Supercharger-turbo_W0QQitemZ200018893476QQcmdZViewItem

It looks like its some sort of DC motorised system that pushes more air in like a little compressor - but doesn't use the engine's power to do so?

It seems too good to be true (these things usually are!) but I thought I would ask if anyone had tried one or knew anything about them

Kind regards

the amount of "extra" horsepower you might pick up from this would proably be solely because of the filter and not the radio shack fan that runs off double a's. Seriously, people running 7 psi only get like 40 horsepower at the rear wheels. and thats including all the "engine draining". If that thing can do 2 psi, its by them duct taping the hell out of everyhting to make it air tight without the engine running (just pressurizing the system). because with the suction of any engine would out power that tiny fan. I have heard of people forgeting to take off the plastic from around a new aftermarket filter, and the intake hose just colapses instantly. Dont get that thing.

[MNBoxster]

Hi,

While conceptually anything which forces more Air into the intake will work, there are no free lunches.

A Standard Supercharger has some issues, mainly Turbine inefficiencies, and it is tied in some way to the revs of the Crankshaft and creates a Parasitic Loss of Crank Horsepower.

As an example, the Supercharger on the Jaguar XK8 draws 76 HP at full boost, but it raises power output by 100HP doing so. Now, if you had an electric SC which required 76HP worth of Amps to operate at full power, it'd take considerably more than 76 Crank HP to produce those Amps by the Alternator.

The problem with the electrics is that Electric Motors are limited in their power output/size. That is, it takes a pretty big motor to make more than a couple lbs. of boost, usually too large for the engine compartment. So, anything which does fit, is going to be limited.

And, while the Elec. Supercharger does not draw Crank HP, the Alternator which powers it does. And, these inefficiencies are compounded - those of the SC along with those of the Alternator. Now, there is a formula for the Amps needed to power the SC motor and one which determines the Parasitic loss at the Crank by the Alternator to produce those Amps, but it's late and I don't have all the necessary variables to do an actual calculation.

One of the advantages to Alternators over the previous Generators is that unless there's a demand, the Alternator almost Freewheels, that is draws minimum Crank HP. But, once there's a heavy demand, the Alt. draws Crank HP much greater than the load requires due to it's inefficiency. Much of this Crank energy is lost as Heat. Also, there's a limit to the number of Amps the Alternator can produce, and to save fuel, Manufacturers don't usually oversize them by much. So, with accessories, AC, Lights going, charging the Battery, and such, there may not be enough Amps left to power a SC anyway.

I'm afraid in the end, this device won't live up to it's claims and so is essentially a waste of money. Hope this helps...

Happy Motoring!... Jim'99

[oliverg]

you guys are a wealth of information. thank you very much for sharing it.

its a shame that these "auto snake oil" products can be sold legally. they shouldn't be able to make such claims without having to be put up to some scrutiny.

much respect, Oliver