I don't think anyone's put their car on the dyno and checked HP results but there have been a couple forum members that have gone to the track after installing one and shown that they do work. We're obviously not talking about a huge ammount of difference but definitely quicker through the 1/4 from their last runs without the pulley.
The problem with them is that if your charging system is starting to become old in any way it will show up right away after installing one. People are content that their charging system is working as long as their cars gauge is showing it charging. This isn't necassarily true though. It's a very very good idea to check out your charging system before installing a pulley and make sure the alternator and battery are doing what they're supposed to do with a real meter outside the car. Also a very good idea to clean all the contacts and grounds.
I put a pulley on my old car and it had no problems. I had a new alternator and battery though. I could definitely feel a difference in acceleration but have no actual track or dyno proof of this. I do intend to put one on my current Fiero very soon.
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Activities Director N.I.F.E.
