underdrive pulleys

My friend said that underdrive pulleys are no good to have, all they do is wear the belts more...Is this true?

i dont' know aobut belt wear, but i do know theya ren't good to have due to the extra strain put on the crank shaft. This also takes a lot of power away form your headlights and stereo if you haev one

Thos pulleys can be good for a motor that is built for it. Other wise they do put alot of strain on your motor.:(

and how do you build an motor to handle the pulley?

probably a lightweight crank and good bearings? mains?

by underdrive pulleys do you mean a new crankshaft pulley? im asking for me, im not accusing you of being wrong - i have no idea. i got the AEM trupower pulley set and only installed the pulley for the water pump. does anybody know how much power the alternator pulley will take off? like what %? im going to need like 200 amps, not sure if ill ever be able to use that 2nd pulley.