Today I was told the UD pullys are no good and will not or barely work with the altinator. I was told i needed another smaller pulley, any truth to this?
It makes sense...If you underdrive the crank, then the accessory pullies are moving at a slower speed just due to mechanical advantage and whatever. I suppose it isnt out of the realm of possibilities to not run the alternator well. But I have an UDP with the stock alternator pully and I dont have any trouble. Problem is, most of the crank pullies your gunna find dont come with an alternator pully if you wanted one. But Im almost 100% sure that everyone here will tell you it wont matter.
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96': Rebuilt 3.8, Hurst short throw, eBay CAI, Taylor wires, Eibach Sportline Springs, Tokico shocks, Steeda C/C plates, ASP udp, H-pipe dual exhaust w/ Flowmaster 40 Series
I have not done it myself, but I think you can measure with rope and get a smaller belt. I agree with the theory but I don't know if the slight gain would be worth the trouble.
Posts: 11551
Joined: 9/19/2005 From: Pearl River, Louisiana Status: offline
Only 5.0s have the alternator charge problem and that has since been addressed in newer U/D pully sets. Your car will be 100% fine with the pullies, even on a modestly large stereo system, although anything over 500 total Watts may require a few more things, and over 750 may require a larger alternator, but that's beyond what we're talking about. All in all, you'll be fine, however, don't expect to see any noticible power difference. It will show on the dyno, but not the track.
Posts: 1758
Joined: 1/12/2007 From: Eureka, Ca. Status: offline
I put a 25% UDP on my car then checked the alt at idle and it was fine. The only problem I had was the pulley itself wasn't timed correctly so the car would run crappy and it threw a code so I kept the stock pulley on it.
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My 04 Mustang is a hybrid, it burns gas and rubber.
I had the motoblue UDPs for a year. You want notice a major performance gain with UDPs. Accept that your lights will burn alittle dimmer and the vents will blow alittle weaker. UDPs really arent worth it. Maybe as a last resort mod when everything else has been done and you are trying to optimize the performance and squeeze every bit of it out.
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"UD pulley nogood" says mechanic - 
