UD Pulleys and Alternator Output

[justin00v6]

We had a little discusion about this a while back, but I never did any real world testing.

Today I put an ASP 25% UD crank on a 99 3.8. The car is a 5spd and idles at 700rpm.

You want to see 14-14.4v from an alt, depending on temperature. Anything lower than 13.75-13.5v for more than say 15-30sec IMO and you will wear out the battery faster.

His car at idle 14v. But once you turn on the headlights, engine fan, ac on high you drop to 13.5v, and then drop maybe .1v/30sec. With the brake lights you drop to 13v and then maybe drop .05v/min. Once voltage goes down to 12v or so you stop dropping.

With an auto it idles lower in drive and you would be even worse off.

I put a 14% OD alt pulley on his car. With everything above on the voltage stayed at 14v. Hitting the brakes dropped it to 13.75 then slowly to 13.5. If you turned the ac to low and hit the brakes then voltage stayed close to 14v.

So with a 14% OD alt pulley on 5spds idling at 700rpms the situation is decent.

For autos I would want at least a 20% OD alt pulley, but you could make due with less worst case.

The above testing did not take into account defroster or foglights. The defrost pulls a ton but most people don't use it much.

Now lets talk about what is available:
For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.
mid 99-03 has to use this very expensive OD alt pulley which is like $42 and is 15% OD (OEM through non-dealer channels)

98 4.6 GTs have an alt pulley that is 15% OD for us...I'm pretty sure that 96-97 do not have this size alt pulley. Ford does not service the pulley seperately. So you are kind of limited to junkyards and GT owners who installed the full UDP set.

If you can score a 99+ GT alt pulley you would be doing good, it is 20% OD and about 2" in diameter, same deal as above though.

Both of the above GT pulleys will work on all 94+ 3.8s.

ASP makes an OD alt pulley that is 1.7" and 32% OD but it slips like a mofo, lots of belt dust. I ran one for a while and it worked but if the belt got wet (driving through big puddle) charge would drop out for a minute while it dried. I don't recomend going that small. Will work on 94-mid 99 though.

Some people have an UD crank and they are fine....its just those repeated high drain situations that will kill the bat faster.

ASP and MAC make 94-98 UD pulley sets that come with an Alt, but I don't know why they bother, their alt is only a 2% OD and barely smaller than stock.

Hmm I think that is all.

[Bloodninja]

Hmm, that sucks. I do a fair amount of idling in traffic with the a/c, brakes, etc.

I may be able to source a GT pulley. Do any of these necessitate a new belt?

[justin00v6]

Hmm, that sucks. I do a fair amount of idling in traffic with the a/c, brakes, etc.

I may be able to source a GT pulley. Do any of these necessitate a new belt?

yeah, i killed a dynabat in a year with a 25% ud crank

nah, alt pullies don't make enough of a size difference to warrant a diff one

[Jared]

i bought the crank and alt pulley from you. i noticed a good diff in alt. voltage after the OD alt pulley. saved alot of life in my alt.

[BlackStang95]

I have a 94 with ASPs pulley and I run my defrost, lights, fogs, and loud stereo with no problems so far. I don't use the a/c much though.

Underdrive pulleys rock :headbang:

[justin00v6]

I have a 94 with ASPs pulley and I run my defrost, lights, fogs, and loud stereo with no problems so far. I don't use the a/c much though.

Underdrive pulleys rock :headbang:

Put a voltmeter on it with all of the above on at idle, i bet you are at 13v or lower.

For the sake of comparison I checked out a 95 5spd with stock pulleys. It idled around 550rpm. With headlights, AC high, engine fan, and brake lights, it never dipped below 14v.

[zbgsaa]

so how would this all play if you also had a system pulling 800w off a stock alt.

what would you recommend if i wanted an UD pulley as well as an OD pulley?

[Bloodninja]

If you can score a 99+ GT alt pulley you would be doing good, it is 20% OD and about 2" in diameter, same deal as above though.

Both of the above GT pulleys will work on all 94+ 3.8s.


Great, straight bolt on? Is the pulley just a bolt? I don't know, I haven't
removed a pulley before.

I found a guy willing to give me a 99 gt alt pulley and i'll be installing it
with my underdrive hopefully this weekend.

[justin00v6]

If you can score a 99+ GT alt pulley you would be doing good, it is 20% OD and about 2" in diameter, same deal as above though.

Both of the above GT pulleys will work on all 94+ 3.8s.


Great, straight bolt on? Is the pulley just a bolt? I don't know, I haven't
removed a pulley before.

I found a guy willing to give me a 99 gt alt pulley and i'll be installing it
with my underdrive hopefully this weekend.

str8 up

[Bloodninja]

str8 up

str8 w3rd

[fr0IVIan]

??? how does the alt pulley bolt come off... it spins with the pulley...

[justin00v6]

??? how does the alt pulley bolt come off... it spins with the pulley...

impact gun for on and off

[BlackStang95]

Yeah...if im gonna idle for very long with lots of stuff going I usually rev it up to around a thousand or so. You said it gets full charge at 950.

Are you saying my batteries gonna die? :eek:

[SLOPEL]

justin, do you have an asp alt OD pully for my 94?

[pb_milan]

??? how does the alt pulley bolt come off... it spins with the pulley...

impact is the only way.

[zbgsaa]

when you did this testing did you use a digital, analog multimeter, or just estimation?

and if you used a multimeter where did you use to test the + ?

[Flex]

Would the difference between the 94 and the 99 have anything to do with the alternator? Maybe the 94's alt. puts out more power?

[RobertKnapp]

So if you put a 20%OD and a 25%UD isnt that only a 5% UD??

I got just a little play money the other day, not much for anything significant but pulley's for sale by someone else is doable. However, my big *** stereo is what Im concerned about.

[RobertKnapp]

So if you put a 20%OD and a 25%UD isnt that only a 5% UD??

I got just a little play money the other day, not much for anything significant but pulley's for sale by someone else is doable. However, my big *** stereo is what Im concerned about.

everybody says pulleys are the cheapest and most recongizable mod but not at the expense of my stereo! say it aint so

[Flex]

No Rob,
If you under drive the crank pulley %25, you are underdriving the entire system that much. By OD the alternator, you would in essence be OD 'ing it alone and the rest os the system would still be at %25 UD

[zbgsaa]

when you did this testing did you use a digital, analog multimeter, or just estimation?

and if you used a multimeter where did you use to test the + ?

?????????????????????????????????????

[justin00v6]

when you did this testing did you use a digital, analog multimeter, or just estimation?

and if you used a multimeter where did you use to test the + ?

?????????????????????????????????????

I used a digital multimeter, a Fluke. I put them both on the battery...all the wires in the system are big, and the alt has a direct line to the battery.

[zbgsaa]

but dont you think you would see an increase in voltage at least under heavy load if these wires were graded to say 4 ga?

[99whitestang]

For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.


Does this change correspond with the "notch" change?

Is the aftermarket one you speak of previousily the ASP one? If not ASP who makes this one?

Why does the '94 alt. pull different voltage with same amount of drain? :confused: did you use the same gauges for both tests?

[justin00v6]

For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.


Does this change correspond with the "notch" change?

Is the aftermarket one you speak of previousily the ASP one? If not ASP who makes this one?

Why does the '94 alt. pull different voltage with same amount of drain? :confused: did you use the same gauges for both tests?

You'll have to pull your alternator pulley off to find out. Its ASP. Becauset he 94 had STOCK pullies and the 99 I tested had an UD crank and then we put an OD alt on it. I used a Fluke.

[99whitestang]

For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.


Does this change correspond with the "notch" change?

Is the aftermarket one you speak of previousily the ASP one? If not ASP who makes this one?

Why does the '94 alt. pull different voltage with same amount of drain? :confused: did you use the same gauges for both tests?

You'll have to pull your alternator pulley off to find out. Its ASP. Becauset he 94 had STOCK pullies and the 99 I tested had an UD crank and then we put an OD alt on it. I used a Fluke.

So the '94 didn't have the ASP pulley on it, so have you tested a '94 with the ASP on it? I was just wondering if they had changed them over the years at all? Do all Mustangs have the same alts? I was wondering if maybe a Cobra alt is more powerful and could be swaped easily?-just a thought...I am not real eager to switch to the ASP alt. pulley after what you said, "they slip like a mofo", my car has enough slippage and rattles etc. (problems without adding more) :(

[justin00v6]

For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.


Does this change correspond with the "notch" change?

Is the aftermarket one you speak of previousily the ASP one? If not ASP who makes this one?

Why does the '94 alt. pull different voltage with same amount of drain? :confused: did you use the same gauges for both tests?

You'll have to pull your alternator pulley off to find out. Its ASP. Becauset he 94 had STOCK pullies and the 99 I tested had an UD crank and then we put an OD alt on it. I used a Fluke.

So the '94 didn't have the ASP pulley on it, so have you tested a '94 with the ASP on it? I was just wondering if they had changed them over the years at all? Do all Mustangs have the same alts? I was wondering if maybe a Cobra alt is more powerful and could be swaped easily?-just a thought...I am not real eager to switch to the ASP alt. pulley after what you said, "they slip like a mofo", my car has enough slippage and rattles etc. (problems without adding more) :(

Your last two posts on this thread have showed that your reading comprehension sucks. I don't know how else to put it.

The 94 had stock pullies, like I said several times before. All 94+ mustangs have the same 3G 130amp alternator (though slightly different cases for 01+). The 4.6 alts will not fit our cars, and I think they are probably the same. If you read closely you'll notice that I said the 1.7" 32% OD alt pulley slips like a mofo (but you'll never hear it squeel). The 14-20% OD alt pulleys will not slip badly.

[crabmeat]

:confused: :confused: :confused: it's a friggin 12v system.....designed to run on 12v. i have a vert and with AIR COND on, lights on, radio blasting when i put my top up i saw no major movement or diming of the lights. a 25% pulley is ok. if your worried about the battery got to sears and get one of thos truck die hard things or get a marine battery.

peace :banghead: :banghead: :( :(

[zbgsaa]

:confused: :confused: :confused: it's a friggin 12v system.....designed to run on 12v. i have a vert and with AIR COND on, lights on, radio blasting when i put my top up i saw no major movement or diming of the lights. a 25% pulley is ok. if your worried about the battery got to sears and get one of thos truck die hard things or get a marine battery.

peace :banghead: :banghead: :( :(

lol why would you have the air on putting the top up?

:confused:

[justin00v6]

:confused: :confused: :confused: it's a friggin 12v system.....designed to run on 12v. i have a vert and with AIR COND on, lights on, radio blasting when i put my top up i saw no major movement or diming of the lights. a 25% pulley is ok. if your worried about the battery got to sears and get one of thos truck die hard things or get a marine battery.

peace :banghead: :banghead: :( :(

Cars are actually a 14v system (varies a little bit with temperature), the regular in you alt keeps things around 14v +/- .2-.4v. If your alternator's overall output drops low enough to start pulling power from the battery and does that long enough you wll kill the battery, I've been there and killed 2. Sure batteries are designed to be discharged but if you drain alot and do it over an extended period of time they will weaken from doing that repeatedly. Such as sitting at idle for a long time with everything on with an UD crank and no OD alt.

[Flex]

I think he did that to test the sytem dude.

Justin is right. Every time you discharge the battery, you damage it which makes it weaker.

[SpectorV]

I just got an ASP ud pulley. I BARLY ever run the AC or anything like that, usually just listening to the radio and using the brakes. Will i have a problem on my 01 from this? I dont want to screw up my battery. I dont spend much time sitting idling, traffic is usually pretty good here. And will my idle go down? I dont want it to go anylower cuz it gets rough, now its 750~ rpms.

[justin00v6]

I just got an ASP ud pulley. I BARLY ever run the AC or anything like that, usually just listening to the radio and using the brakes. Will i have a problem on my 01 from this? I dont want to screw up my battery. I dont spend much time sitting idling, traffic is usually pretty good here. And will my idle go down? I dont want it to go anylower cuz it gets rough, now its 750~ rpms.

The AC turns on the engine fan which draws tons of power (30-35 amps) then you've got maybe 5-10amps from the blower motor. So if you don't use the AC much at idle then you'll probably be fine.

If you really want to know then put a multimeter on the car and check the voltage. 13.8-14v is fine IMO

[SpectorV]

thats good, i mean i BARLY ever run it, only when i just have to will i turn it on. and if i am at a stop i will just hold the rpms up higher while its on to keep it charging. I just dont want issues from the pulley.

[99whitestang]

For 94-mid 99 you can get a 14% OD alt for $20 (aftermarket)
In mid 99 or starting in 00 they changed to a different style alt snout, the above pulley won't work.


Does this change correspond with the "notch" change?

Is the aftermarket one you speak of previousily the ASP one? If not ASP who makes this one?

Why does the '94 alt. pull different voltage with same amount of drain? :confused: did you use the same gauges for both tests?

You'll have to pull your alternator pulley off to find out. Its ASP. Becauset he 94 had STOCK pullies and the 99 I tested had an UD crank and then we put an OD alt on it. I used a Fluke.

So the '94 didn't have the ASP pulley on it, so have you tested a '94 with the ASP on it? I was just wondering if they had changed them over the years at all? Do all Mustangs have the same alts? I was wondering if maybe a Cobra alt is more powerful and could be swaped easily?-just a thought...I am not real eager to switch to the ASP alt. pulley after what you said, "they slip like a mofo", my car has enough slippage and rattles etc. (problems without adding more) :(

Your last two posts on this thread have showed that your reading comprehension sucks. I don't know how else to put it.

The 94 had stock pullies, like I said several times before. All 94+ mustangs have the same 3G 130amp alternator (though slightly different cases for 01+). The 4.6 alts will not fit our cars, and I think they are probably the same. If you read closely you'll notice that I said the 1.7" 32% OD alt pulley slips like a mofo (but you'll never hear it squeel). The 14-20% OD alt pulleys will not slip badly.

Your last two posts on this thread have showed that your reading comprehension sucks. I don't know how else to put it.

Actually what confused me about this is I had 2 different people e-mail me and ask if I had a '96-'98 GT (4.6L) alt. pulley that would fix the pulley proablem, I am not sure if they were from this board or another one, but between that and reading a bunch of posts I misunderstood...

The 14-20% OD alt pulleys will not slip badly. so this will fix the problem and keep the alt. power @ or ~14v (where it should be) and not kill the battery faster? Who makes this part ASP? How much is this thru u (VMP) for the notched '99 version?

Sorry but I am not worried about having the ASP pulley by itself on there running, I want my battery and alt. to last as long as possible, it made me really concerned when a friend of mine replaced the alt. in his Chevy Tahoe and it cost $600 at the Chevy dealer... :eek:

Justin-e-mail me this info if you want

[99whitestang]

-ttt-

Sorry to push this back up but I don't want to buy a new battery anytime soon, and I want my car so its charging right...I guess Justin is pissed off at me, he will not e-mail me the answer to this, so if anyone else knows please tell me (see above post for my question)

Thanks! :)

[justin00v6]

Clearly, you need to email me when you don't get a response on the board. I don't read everything on v6p.

[99whitestang]

Clearly, you need to email me when you don't get a response on the board. I don't read everything on v6p.

I sent you an e-mail. :)

[RGR]

:confused: :confused: :confused: it's a friggin 12v system.....designed to run on 12v. i have a vert and with AIR COND on, lights on, radio blasting when i put my top up i saw no major movement or diming of the lights. a 25% pulley is ok. if your worried about the battery got to sears and get one of thos truck die hard things or get a marine battery.

peace :banghead: :banghead: :( :(

true, but you have to produce over
12V to charge a 12V battery, hence
the 14V regulation of the system.
Load also reduces voltage somewhat.