I am thinking about getting a 25% underdrive pulley for my car.

I do drive it very often in the summer. Not always short trips but not always long trips either. I have heard that there are concerns about the system charging. I do have a pretty fresh red top optima in the car if that matters.

Are there any other downsides and is this upgrade if I buy a used one worth the money?

 

Possible belt slippage, depending on the brand. Which one are you looking at? SLP/Powerbond is probably the best "middle of the road" 25% UDP.

 

I haven't really decided which one to get yet (kinda needed that advice too)

But I definitely had heard most of those 2 brands. By default I was probably going to look at SLP

 

If you have a stock cam I would skip it. If you have an aftermarket cam and accompanying raised idle then I might consider it.

Optimas have gone way way downhill in recent years I wouldn't use that as an argument for being OK at idle but rather against being OK at idle with a stock cam.

 

I have driven in my SLP pulley for a little over a year and no charging issues. That being said, I'm carmed and it idles a little higher at 900 rpms. Stock at 600rpms, possibly....You're in luck though as I'm selling mine. The f-body accesories are not cooperating with my Detroit speed frame, so I'm moving over to corvette accesories and requires a different pulley

It's in the swap meet section for $150 shipped, only a little over a year old.

 

Ok thanks guys. I do plan on camming it but all depends when I have the money and stuff. I'll think about it but yeah I don't really want to create problems when my car already runs perfect.

My car does idle higher than 600 it's more around 900 I really don't know why though. I will be sending it out to Frost to get a mail-order tune for now since it isn't a full-out race car... just a bolt-on street car with occasional strip use. Maybe that will fix the idle or maybe that's just where my car likes to be, who knows.

 

Is the idle verified or trusting a stock tach?

 

^^This..stock tach is not accurate. And I and my buddies all run 25% with no issues from stock to wild.

 

Cheap easy bolt on. Most folks have a UDP

 

Thank you.

 

Good point guys, trusting stock tach but it does sound like a high idle... probably cause of the small stock cam in the 02 tho?

 

Sounds like good results with factory charging needs. What if you add a stereo/amp?

And what about power steering/AC, water pump?

 

With a M6 transmission the factory idle is 800rpm. So there's no need to raise the engine idle rpm. With a A4 transmission the idle rpm is a lot lower (550-600 rpm) so I'd recommend raising the idle up at least 100rpm to keep the alternator turning at least close to the stock rpm when using a 25% UD crank pulley, if you have issues.

 

March 25% UD. No issues whatsoever/ 5 years. I did not use the accompanying small alternator pulley.
It has stock idle/800, and charges @ 13.5v.

 

I have a stock internal motor in my 2000 ws6. I have the slp under drive pulley. No problems at all.

 

And did you guys have a noticeable increase in performance by using it? Was it worth the money that you spent? Thanks in advance

 

Bumping out of curiosity...

 

Do not raise the idle with ud pulley!
Do a slp/powerbond never look back! Also pick up arp crank bolt...

 

I've always "heard" of issues but never actually seen any. My ati is awesome hands down the best UD they make. The 25% ud ones make the same power as the 10% ati but dont dampen well

 

Aftermarket stereo and a pulley would make me nervous at idle. I have a powerbond 25% and it's fine, blower speed is a little lower at idle when I have the AC ranking during the summer. Volts just drop a little bit at idle and full fan.