What’s Everyone’s Opinion On Underdrive Pulleys?

BlakeusMaximus · Nov 12, 2017

When I was younger, (not knowing ) underdrive pulleys were a cool mod to put on. Now, not so sure. Just curious what you guys think?

a91what · Nov 12, 2017

Useless junk.

Bullitt347 · Nov 12, 2017

Depends on the application. I have an underdrive crank pulley on my 08' Bullitt, but the rest of the pulleys are stock. Never have had an issue with them. I had underdrive pulleys on the 01' V6 Mustang when I owned it, crank, alt and water pump and had no issues during the 60K plus miles I put on the car. I ran a 4" alt pulley on the racecar, but then again it did have a 9.5" crank pulley lol.

BlakeusMaximus · Nov 12, 2017

I’ve never had a problem either, what makes them useless junk? Like I said, just curious. I know about that charging issues.

Mustang5L5 · Nov 12, 2017

I use them. I put some thought into my setup. I run an overdrive ALT pulley and 3G alt. My cooling system is pretty beefy. No charging or cooling issues at all. Pretty reliable for me over 20 years they have been on the car. I also prefer firmer steering so I don't mind undersriving my P/S pump

a91what · Nov 12, 2017

For the average user they usually make more trouble than they are worth. Some find them useful I use underdrive for my ps pump. As long as the application is correct they serve a function

mikestang63 · Nov 12, 2017

waste of money

BlakeusMaximus · Nov 12, 2017

I’ve had a set on pretty much every one of my mustangs over the years and I’ve had four of em. I’ve just transferred them over to each car as I sold em. Back when I was younger, I’m 37 now, everything I heard and read it was a way to free up some hps, and can’t really say I’ve ever felt a difference. Ive read some posts on here lately that they were a waste and just started to wonder.

Mustang5L5 · Nov 12, 2017

If I didn't already have a set, I wouldn't buy them. I run then because I have them.

I do have a set of stock pullies, and after my H/C/I swap, if I have any issues with cooling the stockers will go back on without hesitation.

General karthief · Nov 13, 2017

It's one of them mods that free up a small amount of hp, the mod by itself won't be felt on the butt dyno, if you add four or five little mods at say five hp each thats ten hp, it adds up, as far as using them, I have a set on mine, I had to change the alt pulley because of over charging issues, other than that no big deal. I have mixed feelings about them.

BlakeusMaximus · Nov 13, 2017

I still have a stock set and wondered about putting them back on. I really don't drive my car at night, but when I do that's when I start thinking about putting the stockers back on. Especially when your sitting at a stop light with lights on, blinkers on and heater running. Other than that maybe when I have to change a belt or something like that ill put them back on. Im starting to get mixed feelings about them myself.

Mustang5L5 · Nov 13, 2017

I agree with that thought. I don't drive my car at night, never need to run the heat since I drive in the summer. A/C currently isn't on the car..yet. So right now my actual load is pretty low.

If any of that changes and I start to notice a problem, stockers go back on. To me reliability is #1 vs 3-5 HP. That's why I'm putting TFS heads on anyway.

BlakeusMaximus · Nov 13, 2017

Yes sir!

Boostedpimp · Nov 13, 2017

I've used them on four different foxes with great success... but for the average owner they can tend to expose the weakest links in there charging and cooling systems

BlakeusMaximus · Nov 13, 2017

Yep, never had an issue with em and ive had em on 4 foxbodys as well. I drive at night once in a blue moon, and really only drive the car couple times a month, usually during the day. But with the time change its dark here at 5pm so that's what go me thinking.

88LXSleeper · Nov 13, 2017

I drive mine hard and to several track days, the possibility of creating a problem I would not even think of using them.

95BlueStallion · Nov 13, 2017

Never felt any gain from them on the only car I used them on, so Ive never bought them for others. Have no plans to put them on my current car.

FastDriver · Nov 14, 2017

For fox-bodies, I'm not a fan. I would not do them again. Foxes start out with barely adequate charging and cooling. Underspinning the PS or A/C is not a problem, though. Once you've significantly modified the cooling system, it probably isn't, either. However, I've learned some things about the alternator recently, and it seems like the people who are doing it right all compensate by spinning the alternator with an overdrive pulley on the alt or the crank, anyways. So, I don't ever plan to underspin a alternator again.

Ryuk · Nov 14, 2017

Had them for a short time on my old car. Never again.

Boostedpimp · Nov 14, 2017

FastDriver said:
For fox-bodies, I'm not a fan. I would not do them again. Foxes start out with barely adequate charging and cooling. Underspinning the PS or A/C is not a problem, though. Once you've significantly modified the cooling system, it probably isn't, either. However, I've learned some things about the alternator recently, and it seems like the people who are doing it right all compensate by spinning the alternator with an overdrive pulley on the alt or the crank, anyways. So, I don't ever plan to underspin a alternator again.

a set of pulleys will slow down your accessories including your alternator so most people experience problems getting full charge at idle. Swapping to a smaller aka overdriven pulley for the alternator cures that.

What’s Everyone’s Opinion On Underdrive Pulleys?

BlakeusMaximus

Still got to try a little lube on my speedo head

a91what

SendMeUrDataLog

Bullitt347

I have been doing it wrong this whole time

BlakeusMaximus

Still got to try a little lube on my speedo head

Mustang5L5

That is…until I whipped out my Bissell

a91what

SendMeUrDataLog

mikestang63

BlakeusMaximus

Still got to try a little lube on my speedo head

Mustang5L5

That is…until I whipped out my Bissell

General karthief

wonder how much it would cost to ship you a pair

BlakeusMaximus

Still got to try a little lube on my speedo head

Mustang5L5

That is…until I whipped out my Bissell

BlakeusMaximus

Still got to try a little lube on my speedo head

Boostedpimp

BlakeusMaximus

Still got to try a little lube on my speedo head

88LXSleeper

Active Member

95BlueStallion

My assy trans to myself

FastDriver

I was uncomfortably high & wearing a helmet

Ryuk

I love your drawers

Boostedpimp

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