Underdrive Pulley Question

**WS6ICK** · 12-13-2008, 07:37 AM

For the guys who are running underdrive pulleys, Are you running an overdrive pulley on your Alternator? Do you have any charging issues? Its going on my 2000 Trans Am, WS6, A4.

**mbrownin** · 12-13-2008, 12:11 PM

Running an ASP underdrive on my 2000 SS M6, stock alt. pulley. Idle speed set to 650, no charging issues.

**WS6ICK** · 12-13-2008, 12:24 PM

Some say that I should run a overdrive pulley on my alternator because its an A4.

**mbrownin** · 12-13-2008, 06:38 PM

I would try it without it first since the alternator overdrive pulley partially negates the benefit of the underdrive pulley. If your system discharges too much at idle and you spend a lot of time at idle, then get it later. This of course assumes that an overdrive pulley does not require a different sized belt. I don't know about that one.

**NaviDyn** · 12-14-2008, 06:02 PM

I ran underdrive pulleys on an old 5.0. I didn't change the alternator pulley for obvious reasons. But even with the much smaller crank pulley, it charged fine. On a motorcraft.

**Firebirdjones** · 12-15-2008, 11:44 AM

I had the underdrive pulley on my 02 SS. I didn't care for it much and it didn't yield me any performance that I could measure so it came off.

Mine is also an automatic. I never did install an overdrive alternator pulley, I felt that it had the opposite affect of what I was trying to accomplish with underdriving everything. I did set the idle speed up a tad to help but I still had dimming lights at night when idling,,,and if the A/C was on it was worse. That was more of a bother to me, didn't have any dead battery issues. What I did have that I could not tolerate was the fact that it turned the water pump so slow that while idling around town the fans would constantly run and struggle to bring down the engine temp. Especially if I were running the A/C... Even with fans only set on 185 degrees they wouldn't shut down unless I was moving at a constant speed with higher engine rpms,,,idling was just too slow for the pump to cool the motor. Once the stock crank pulley was reinstalled,,,,like magic the fans would cycle as they should and cooled the engine no problem. This was while living in Ohio. Now that I'm in Arizona I could only imagine that problem being even worse.

**cuzimoto** · 12-15-2008, 05:48 PM

have had the ASP underdrive for 6 years, no charging problems at all.

**wildbanshee** · 12-16-2008, 03:49 PM

slp underdrive...no problems..actually i would say it made a bigger difference on my car than slp air lid...

**wildbanshee** · 12-16-2008, 03:49 PM

if that means anything...

**PittZ28** · 12-16-2008, 04:17 PM

Originally Posted by WS6ICK

Some say that I should run a overdrive pulley on my alternator because its an A4.

i have an asp on my car and its an a4 and i dont have any problems - it goes to the "begining of the red" when @ idle butother than that nothing. I dont have the alt. overdrive either. I heard that should be used for things requiring more amp draw like a bigger stereo etc.

hope this helps,

Bill

**Bouvers** · 12-16-2008, 04:36 PM

Plenty of people have ran it without the Alt. overdrive pulley and have been fine but if you're running more accessories then you should.

my beef is on my dd my alt. was screwed and it was charging 25% less then it should... which is exactly what and underdrive pulley will do... so kind of leads me to go with an alt. overdrive pulley... just my .02$

**Jays00ss** · 12-19-2008, 06:37 PM

No chargeing issues with my powerbond. 3 rwhp increase but you can really feel the difference in how fast you reach your powerband. Very good mod and I would highly recommend it.

**karpetcm** · 12-20-2008, 04:25 PM

Which is the cheapest pulley and do they all work just the same ?

**SS02** · 12-20-2008, 04:33 PM

I have pulley set with the Alt over pulley, it might have
been in my head... Yet I swear it made a diff at pedal!

Not probs at all.

I had that dynod with other mods so not sure on the HP increase?

**slpdablueZ28** · 12-21-2008, 08:38 AM

what do overdrive and underdrive pulleys do exactly and wats the difference between them?

**mbrownin** · 12-21-2008, 10:55 AM

Originally Posted by slpdablueZ28

what do overdrive and underdrive pulleys do exactly and wats the difference between them?

The main "underdrive" pulley replaces the stock pulley that is attached to the end of the crankshaft. It has a smaller diameter than stock, which means for any given engine rpm, it causes the belt to travel less distance, which in turn causes all the belt-driven accessories (alternator, water pump, power steering pump) to turn slower, thus soaking up a lower percentage of the engine's power.

**Justin93** · 12-21-2008, 10:58 AM

I have the powerbond 25% UD Pulley and have zero alternator issues. It revs faster. Also I have a red top optima under the hood so i've noticed no drop in voltage

**slpdablueZ28** · 12-21-2008, 11:00 AM

Originally Posted by mbrownin

The main "underdrive" pulley replaces the stock pulley that is attached to the end of the crankshaft. It has a smaller diameter than stock, which means for any given engine rpm, it causes the belt to travel less distance, which in turn causes all the belt-driven accessories (alternator, water pump, power steering pump) to turn slower, thus soaking up a lower percentage of the engine's power.

ah ok thanks