Under drive pulleys

So I've heard good and bad things about these. What is the verdict on them? As I understand it, things like your AC and alternator will not work at full capacity since they are "under driven". But the flip side is you gain horse power apparently.

Anyone have experience with them? They worth it? Seems like a pretty cheap mod to do.

 

lots of people dont much like the underdriven pulleys, they use the lightweight ones, i have a 1 lb UD pulley on my impreza, i love it, but i do have an 11lb flywheel also, so it revs like a motorcycle, instantly and ive had no problems with steering, or alternation, and i have a 400 or so watt system

 

I run Under drive pulley
Cons:
Idle, it pulls fast on the RPM when you accelerating, not you even seen the needle moving, you can also feel the power.

Pros:
You need shorter belts. And the instrumental will slightly dimmer as well the headlights

The non-underdrive pulley is the same stock size but lighter than the stock oem. 5lbs versus 1lbs

 

Interesting...anyone have a link to a good one to look at for an 05 WRX?

 

I use a perrin lightweight, non underdriven pulley.

It fits all EJ series engines.

 

^^zak is right, I finally realized that the pulleys can fit any Subaru models, I think

 

the Unorthodox racing pulleys are all the same for all subies i believe too.

i have a UR underdrive pulley. first off it wiegh about 75-80% less then stock. as tbone said you do need shorter belts. this is inda trivky cause you have to guess sizes. i am using belts that are .5" shorter.

when i first put it on my car would idle funny (could be form other thigns) but after about a week of driving it works perfectly. i notice a little less illumination in side but still no surges from the stereo. stereo take alot of juice but it keeps up. i have been getting apporx 2-4 MPG better than before. and i rev the slightest bit faster.