I've read quite different. If iirc a motorsport team did a dyno with NO pulleys (that's right no accessories driven) and only got 3 hp at the CRANK. That's little more than 1 HP at the wheel with NO accessories driven (as compared to underdrive where you may drive the accessories at what? 70%?). Not worth it IMO.TheDream21479 said:Actually the underdrive pulleys aren't worthless...they actually make sense if you think about it. I've used them before...its kind of like adding an intake or an exhaust...not an "OH MY GOD!" mod...but you def can feel the difference...the aftermarket pulleys take quite a bit of load off the car...being lighter and stuff....plus they look cool! (well they would if you could see them....You can't see crap under the hood of a BMW)
Although maybe they save you a few pounds off our porky cars.