I installed underdrive pulleys on my 95 Mustang GT, and now the alternator is unable to keep up with the voltage draw. It is especially bad at night when the lights are on. After driving last night in a high traffic environment, I had a dead battery this morning. Does anybody know what is the stock amperage output for the alternator? And what has everybody else done to rectify the low voltage issue with underdrive pulleys? Is a 200amp or 130amp alternator the answer? Thanks for the assistance.

 

I dont know about your year car but the 89-93's are rated at about 65 amp max so at idle its only about 30 or so. The stock alt pulley is smaller so it will spin slightly faster and you could bump your idle up a little otherwise check all your connections. I put a 130 amp alt on mine.

 

your car already has a 130 amp alt. on it, like posted above try setting your idle up a bit

 

you could either put the old alt pulley on the car or bump the idle up some. What is your idle at anyways

 

when you try to mix stock pulleys w/ under drive pulleys, the belt tends not to fit

 

My car idles at approximately 900 RPM when in gear. At idle in neutral it runs about 1000 RPM. Going to order a 200 amp alternator and try to get the voltage/amperage up. If that doesn't work then I will up the RPM's. Going to install a T-5 and get rid of my AODE garbage.

 

you could find a cobra (93) pulley which is smaller than stock I bought one for 15 bux

 

I'm not sure a 200 amp alternator will put out what you want either... it might help a little.. or it might help a lot. High output alternators aren't known for putting out much at idle though. You could always just let your car idle for a minute or two before you turn it off if you think it's going to be a problem

 

What are you trying to power? the 130 amp alt should be plenty. Take it to a parts store they will check your battery and alternator for free.

 

Thanks for the suggestions, going to try to install the original pulley and check the belt length, hopefully the belt will still have good tension. If that doesn't work then will bump the idle up a bit. I had a high amp alternator installed on a Camaro that I once owned and it would only charge at high rpm's, so I have decided against the high amp alternator option. Remember, I live in Japan so parts support and technical assistance is non-existent.