I wanna hear about peoples experiences with them. what are they like? how well do they work? are they worth it.....actually I take that last one back. did you notice any difference at all?

I would consider one if I could find one for a M20. :(

I would consider one if I could find one for a M20. :(
same here :rolleyes

dont know about BMW under drive but i had em for my 5.0 mustang....and yes, they worked...

BUT...

biggest problems with them is that your car has to be in tip top shape, engine cooling wise and charging system wise...

idling at 700 rpm my lights would dim and pulse with the rpm shake of the engine...listening to my sound system for any lenght of time at idle would not regerate the battery if i had the lights and the heating fan blasting...

now...when it comes to BMW's system...i have no clue...

knowing what kind of tolerances bmw uses as compared to fords v8 technology...i'd say the gains are much lower... the 5.0 did pick up 10 whp dyno proven from the pulleys...

dont know about BMW under drive but i had em for my 5.0 mustang....and yes, they worked...

BUT...

biggest problems with them is that your car has to be in tip top shape, engine cooling wise and charging system wise...

idling at 700 rpm my lights would dim and pulse with the rpm shake of the engine...listening to my sound system for any lenght of time at idle would not regerate the battery if i had the lights and the heating fan blasting...

now...when it comes to BMW's system...i have no clue...

knowing what kind of tolerances bmw uses as compared to fords v8 technology...i'd say the gains are much lower... the 5.0 did pick up 10 whp dyno proven from the pulleys...
hmm I wondering If i dont underdrive the alternator just the water pump and the power steering. Ive got a lower C tstat and with a new fan clutch would I have to worry?