oversize alternator pulley or stock?

tommy_1812

New Member
Dec 21, 2005
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Kerrville, TX
Hi everyone. Thanks for the advice in my previous threads. The well rounded and tasteful modifications you all do has helped me to find ideas for my stang.

I have one problem someone could help me with. I upgraded to a 100 AMP Jegs alternator some months ago. I don't run any accessories and rarely drive at night (not much need for headlights). My alternator has the underdrive pulley attached to it. The alt doesn't charge like it should.

Someone told me I could get an oversized pulley for the alternator, but keep my other ud pulleys. Is this possible? If so, which exact pulley should I get. Some of the following are what I found:

Pulleys 79-93 5.0 25%crank/15%WP/1 7/8" Alt, full charge @ 700 RPM,Zinc
Pulley 87-96 5.0/5.8 Ford tr. 52% crank/1 7/8" alt/15% WP full 1200rpm

I'm a little confused about the top two (found them on Summitracing.com).

What's the difference between the two?
 
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getting a bigger/oversized alt pulley will just slow it down more and do exactly what you dont want.

ud pulley kits come with a smaller crank pulley, bigger WP and alt pulleys. the cranks pulley is smaller and its driving the rest of the belt system, a smaller pulley will move LESS belt per revolution, soe the whole belt system turns slower, then on the wp and alt with bigger pulleys. it takes MORE belt to make it make one rotation so it turns slower.

so in a nutshell, the smaller crank pulley slows the whole belt drive down, then the alt and WP turn even slower due to their bigger pullies.

to cure the alt problems, put the stock pulley back on or get a SMALLER alt pulley.