Ive heard that pullys will mess up am oem alternator, is it true?
 

Well, will they?

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90 GT, Red with white racing stripes. Did the AOD-T5 swap, Steeda Tri-Ax shifter, Factory sun roof and armrest delete, Pace setter off-road H pipe, Flows, Ford Racing aluminim driveshaft, Auto Meter Sport Comp Silver tach, and a K&N filter.

They can be hard on them, but i dont think it will actually ruin one? If you let a car idle too long with pullies, your volts can sink donw, the alternator being spun slower, thus making the alternator not as powerful, the street pullies shouldnt hurt, the "race" ones will drain your battery at an idle.

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formerly known "90dpscoupe"
5spd 90lx, 3.27grs, BM fan, alum divesahaft, ADS chip, 160 stat, mac coldair fender, mac h-pipe.
Best e.t-13.91
60'-1.9 (on 225/60/15 firehawks)
mph- 98.70

The underdrive pulleys turn the stock alternator slower so it puts out less amps and this can strain the system, especially at idle with lights, stereo, A/C fan all going at once.

Generally, a stock 75-amp alternator in good condition (with a good battery) can handle it but older ones often have problems.

I would suggest that if you install the pulleys prepare to upgrade to the 130-amp alternator. If you don't need to, great, but if you do, you'll be ready.

I think I'm ready.......I'm just tired of the lights dimming at lights, and I've got an extra $150 after this next round of mods http://www.mustangworks.com/msgboard/biggrin.gif

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'90 5.0 LX - heads, intake, cam, fuel delivery, gears, full exhaust, pulleys, ignition, drag springs, front brake upgrade, a/c delete, K&N cone filter charger.......and much more!
1/4 mile: 12.29 @113
60': 1.78

my ride