underdrive pullies

Yeah, don't worry about something getting "screwed up." The worst that happens is your battery does not charge well or your car runs warmer at idle. Then you sell your pulleys...or as in my case, you swap the alternator pulley back to stock. More power and better fuel economy are the common results of pulleys...more common than the problems, its just people tend to post about the problems far more than they do about the benefits.

....and the unaware have to be careful about swapping other pulleys on and off -- sometimes the results are unintended.

Most underdrive street sets have an alternator pulley that is actually an OVERDRIVE pulley -- smaller than stock -- to speed the alternator back up to some extent. If you take that one off, and put the larger stock one back on, you'll actually slow the alternator down even more exacerbating charging issues. Smaller drive pulleys (crank) slow EVERYTHING down. Smaller driven pulleys (water pump, alt) speed those accessories up. The amount of speed change is directly proportional to the ratio of the diameter of the pulleys being swapped.

The irony here is that MANY folks have added underdrives (about $40-100 depending on new, used, etc.). And then they spend another $300-$600 on 3G 130A alternators, aluminum radiators, electric fans/controllers to try and get the car to charge and cool properly. And, of course, adding the 130A alternator un-does the benefit of underdriving the stock alternator. So you end up spending $500+ for maybe 5HP most of which shows up over 3500 rpm.

I'm thinking that leaving the pulleys, alternator and cooling system stock, and throwing a 100-shot of nitrous on it would be a much better better performance improvement...

Oh - and the reason so many post about problems, is because they happen fairly often. The biggest culprit is charging issues. The stock fox body 65A alternator was marginal for meeting charging needs when the car was stock. Slow it down a bit - and it's an even bigger problem.

Oh - and Matt - if you like cars, there's going to be one heckuva car show April 1st down in Atlanta on Ga. Tech's campus -- the 3rd annual Ga. Tech car show. The turnout and diversity of cars is most impressive...

Mine are aluminum pulleys from Mustangs Unlimited. I noticed a power increase in mine and I like'em. I put the stock alternator pulley back on because charging was lower then I liked. It brought it up some, and I was able to keep the stock belt. They have only been on for about 2mths maybe. I'll see what the long term does, but as of now they are staying on. Mine were $90.00 shipped.