they work by making it easier for the motor to turn the drivebelts. this in turn gives back the HP that was used. they indeed give only a few wheel ponies, but w/ them being colorful, they can be cosmetic. it replaces the alternator & power steering, & some Co.s swap out the crank pulley. AEM kits go for $150-175 (only 2 pulleys), Unorthodox can go as high as $300 (gives 3 pulleys).

the only problem is that sometimes there isn't enuff juice in the alternator to keep a constant flow of electricity, so sometimes the motor stutters. if you plan on running a stereo w/ even 1 amp, don't even consider pulleys.