3.73's and pullies overkill???

U/D pulleys will slow down the accessories, that will help with wear and tear technically.

Gears, longtubes and pulleys are a nice start for a stock car.

Put them on.

If you're running the stock 65A alternator, and have to deal with a/c/hot summers/traffic -- the u/d's may cause some charging and/or cooling issues. No way to know except by trying them. And likely they won't show up til next spring when it starts to warm up again. If the car is otherwise stock, I'd sell the pullies, and put the money towards having tmoss port your stock lower intake. That will work well with your other changes. Weld-in subframe connectors will make a big difference as well.

D's 91 stang gt said:

I just installed and set of 3.73's long tubes and x pipe I love it so far like a whole new car I also have a set of mac underdrive pullies but I'm hesitant to install the because the car is running at higher rpms now so my question is would installing the pullies be even more wear and tear on the engine or should I go ahead and install them?

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UD pulleys spin all the pulleys less revolutions per minute ... it creates less wear overall.

The downside/trade off is the waterpump will flow less gph at idle, as well as the alternator producing less amperage. The typical solution if you run into charging issues is to buy a larger alternator (130amp) that puts out more at idle.

i like the UD pulleys but i ad to upgrade my alt

or dont install your alternator pulley...

stang2841 said:

or dont install your alternator pulley...

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That will save a few amps and might be enough if charging becomes an issue ... but the alternator still rotates a little less than stock, because the crank pulley has a smaller circumference.

Keep in mind that many u/d kits (if not most street u/d kits) have a pulley that's designed to OVERDRIVE the alternator - in order to speed it back up some to avoid charging issues. If you leave that one off - you may actually be making the charging issue worse. The key is compare the alt. pulley diameter to the one in the kit for the alt. If the kit pulley is SMALLER than the stock alt. pulley, then you want to put it on to speed the alt. up.

A smaller DRIVE pulley slows everything down. A smaller DRIVEN pulley (alt. is a DRIVEN accessory) speeds that accessory up.

A LOT of people have added u/d's thinking they were bolting on 5-8HP for about $80. In the end after adding a larger radiator and electric fans to solve cooling issues, and upgrading the alternator to solve charging issues (exacerbated by the electric fans) their cash outlay was more like $500-700 and their HP gain was more like 3hp, and most of that only above 3500 rpm which is achieved pretty rarely in normal street driving.

I would suggest trying the u/d's and see what you get. If they cause problems -- you'd probably be better off removing them and going back to the stock set up.

Intake, intake, intake.....the stock lower is the most restrictive piece on the motor. A port job by tmoss won't cost much more than u/d's -- but will deliver MUCH more without any downside.

I installed a set of March "Power and Amp Series" pullies about two years ago. I have had no problems charging or cooling whatsoever, even with the AC on. Fit and finish is excellent. I also have 3.73's and full exhaust. Great set-up.

D's 91 stang - Here's the most important part of the thread: What happens on someone else's Stang has no bearing at all on what's gonna happen with yours. There are WAY too many variables to make how they worked on one car in certain traffic conditions with certain mods in certain weather patterns predictive of how they're going to work on another.

The ONLY way to know what's gonna happen with yours is to try them.

Michael Yount said:

D's 91 stang - Here's the most important part of the thread: What happens on someone else's Stang has no bearing at all on what's gonna happen with yours. There are WAY too many variables to make how they worked on one car in certain traffic conditions with certain mods in certain weather patterns predictive of how they're going to work on another.

The ONLY way to know what's gonna happen with yours is to try them.

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Mike is right but for the info no problems with my MARCH pullies and stock alternator