[juggalowelder]

I have a 1990 mustang gt. I have a powermaster 130 amp alternator. With that alternator I would be at 13.9 volts nonstop with every accessory on. It was great. I recently just put on a set of MAC underdrive pulleys and it killed my volts. I knew they would drop down, but not this bad. I was told it would be fine by my local speed shop since I had the big alternator. I put on the pulleys, and at best I had 10 volts. Eventually, by the end of the day, the car would die. Because the underdrive pulley for the alternator was bigger in diameter causing it not to spin as much, hence, losing voltage.

So, I put on the stock pulley from the alternator which is about 1/4 inch smaller in diameter, got a smaller belt and had to recharge the battery because it was dead and now I'm at 10.5-11.5 volts. Which is ok, but I would like more.

What I need to know is, are there other alternators out there from other make cars that will fit an alternator for a mustang but be about 1/4-1/2 inch smaller in diameter than stock? This way, the alternator would spin more, giving me more volts. Or does a company make smallers pulleys for this application? I know I can't be the only person with this problem.

Any help would be greatly appreciated.

[1BADSTANG]

i dont understand your question but can i buy your stock pulleys?

[TT86]

If you have a decent parts store near you, you can take the pulley down there, explain your problem, and they can find one for you.... Take a look at this pic of my set up. I am running a 3G ford pulley (small) on a GM 1-wire Alt with underdrives and showing 14.4v over 2K rpm, and 12.9 just off idle... My buddy at the parts store suggested it to me, and it works great, and is easier to wire than the ford unit.

[TENGRAM]

the underdrive crank pulley is also making the alt turn slower. why not just put the stock one back on? putting a smaller alt pulley is just going to negate the gains from the crank underdrive pulley anyway.

[1BADSTANG]

no sell the stock ones to me.

[TT86]

Originally Posted by TENGRAM the underdrive crank pulley is also making the alt turn slower. why not just put the stock one back on? putting a smaller alt pulley is just going to negate the gains from the crank underdrive pulley anyway.

TENGRAM's right to a point. If you are like me, and your belt is only turning an Alt and the waterpump... switch back to stock pulleys.

However; underdrives work their best (provide more power gain) when they are on a full accessory system with A/C, Smog Pump, Alt, H2O pump, power steering... etc...

[TENGRAM]

Originally Posted by TT86 However; underdrives work their best (provide more power gain) when they are on a full accessory system with A/C, Smog Pump, Alt, H2O pump, power steering... etc...

true, but the alternator takes the most power to run, aside from the a/c. the others cost very minimal power in comparison.

[TT86]

Very true...Especially if the battery is low, or dying... I've seen the alt turn so hard, that the belt slipped and super-heated the pulley... lead to many problems.. including not charging....have you checked for belt slippage?? You mentioned you got a new belt, are you sure there is enough tension on the new belt??

[juggalowelder]

The belt is plenty small. Since I put the stock pulley back on, that is only a 1/4 inch smaller, and I put on a belt that is 1 inch smaller. So, that's not the problem.

The fact of the matter is that Since the crank pulley is changed, the stock pulley still isn't spinning fast enough. Changing it to a smaller pulley will eleviate this problem.

I currently have a powermaster 130 amp 1 wire hook up alternator on there. I will go to the local store tomorrow and see what they come up with. I just think that I need a pulley thats 1/4 to 1/2 inch smaller. That way, I keep the underdrives, so I keep the small horsepower gain, but I also will have a good charge.

As for the pulleys, as soon as I get the rest of them out of my friends truck, I'll post it and me and someone will work something out.

Thanks for all the comments back and if anyone has anymore ideas keep them coming. I'm new to this board but here to stay.

For the record, this isn't the only mod to my mustang.
lowered 2.5 inches w/ bbk lowering springs
kyb gas struts
off road h pipe
2 chamber flowmasters w/ dumps out of the mufflers
75-150 shot of nos via compucar system w/ 10lb bottle
msd digital 6 ignition for the nos, timing retarder, rev limiter etc...
msd blaster 2 coil
k&n fender air filter
gauges out the wazoo
17" cobra replicas (1993) black powder coat on the inside
svo style hood
blanked out rear trunk lid
carbon fiber altezza tail lights
new headlights
many, many, more I can't think of.....

[juggalowelder]

I put the original alternator pulley on last nite and it seemed to run fine. I drove it today and it died again. So, I'm thinking. Find a pulley thats a little smaller than stock. The original stock pulley is 2", so if I can find one that is about 1.5" I think would be perfect. We'll see. If that doesn't do it, it's back to the stock pulleys because this is rediculous. I don't understand how this can work on SOME cars and not others for no rhyme or reason.

oh, the new belt is 1" smaller and the difference between the 2 pulleys is only 1/4" so I know the new belt is definitely giving enough tension.

any other ideas let me know..

[sneezingfox]

Man that's a good looking car... and I hate red... Oh and my power master does not charge well either. The factory 65amp worked better that the pm140. My volt gauge looks like I'm turning the car on and off. Changed many batteries, many wires, relocated to the trunk, and still the same probnlem. And I'm on my third pm140. How many amps is a 3g, or can you get them in whatever amperage you want?

[Speedstang302]

Originally Posted by TT86 If you have a decent parts store near you, you can take the pulley down there, explain your problem, and they can find one for you.... Take a look at this pic of my set up. I am running a 3G ford pulley (small) on a GM 1-wire Alt with underdrives and showing 14.4v over 2K rpm, and 12.9 just off idle... My buddy at the parts store suggested it to me, and it works great, and is easier to wire than the ford unit.

^^^ so not needed...you just like showing off the TT's....jealous? no...well maybe a little...FINE yeah im jealous...jerk

[juggalowelder]

my powermaster alternator is fine. Before I put on these hellish underdive pulleys, I was at a steady 14 volts. Even with accessories on. Now, these pulleys killed that to say the least. I'm sure I'm overthinking it but I'm just not sure if I should use a smaller pulley on the alternator or a bigger one to make up for the lack of spin it's getting. Either way, the pulley should only run me $10 once I find it and I think that'll fix the problem.

[TT86]

Sorry man, I won't post up any more pictures of it....

Another note... try running the car for a little bit, then touch the pulley. Is it hot to the touch??

[ryans88gt]

I had a slipping belt once and touched the alt pulley and all I heard was a sizzling sound before I had a chance to pull my hand away. A nice blister developed 5 seconds later.

[TENGRAM]

Originally Posted by juggalowelder I'm sure I'm overthinking it but I'm just not sure if I should use a smaller pulley on the alternator or a bigger one to make up for the lack of spin it's getting.

you're overthinking it. you would need a smaller alt pulley and/or a larger crank pulley. think about the sizes of the stock pulleys relative to your underdrives

[TT86]

Originally Posted by ryans88gt I had a slipping belt once and touched the alt pulley and all I heard was a sizzling sound before I had a chance to pull my hand away. A nice blister developed 5 seconds later.

been there and done that, but I didn't get a blister..... I'm a chef... I
m used to that shit! ! !

[Speedstang302]

Originally Posted by TT86 Sorry man, I won't post up any more pictures of it.... Another note... try running the car for a little bit, then touch the pulley. Is it hot to the touch??

i was just playing bro....that be awesome to have...

[tmoss]

I doubt your problem is the pulley - you've got a voltage regulator issue or some other problem with the alternator. I run a 3g with March UD pullies and have no issues even at idle.

[TT86]

Originally Posted by tmoss I doubt your problem is the pulley - you've got a voltage regulator issue or some other problem with the alternator. I run a 3g with March UD pullies and have no issues even at idle.

I've been around for awhile and I have seen maybe 1 bum alternator.The problem is usually much easier than we all think it is. I still think it is your belt slipping on your pulley..... research this further.... and give me some pics of your rig... maybe some fresh eyes could help too...