underdrive pullies
- Thread starter billyboy1955
- Start date
What they do is turn the ratio with different size pullies to slow down the accesory drive (alternator, P/S, waterpump, smog pump, ect) which leaves more power to go the the rear wheels. Good bang for the buck mod. Street sets won't really change drivability, but if you get a race set, it might not drive the waterpump and alternator fast enough in stop and go traffic.
CarFreakGT
20+ Year Stangneter 
From what I understand, your accessories won't work as well since they're getting less pull. Just be aware so that you don't think something has gone
wrong if you install them. It's normal.
wrong if you install them. It's normal.
I used them on 2 of my cars so far and going on a third in a few weeks - I used steel MAC's for 70.00 (cheap but good quality) I did not really feel any different but my gas mileage improved - go figure - I do notice a little low charge with the lights on at night but the cars run cool with 190* t-stats and never any problems
willys1
Active Member
When installed mine didnt charge at idle,and it took alot longer to cool down after a run at the track.But there is a noticable performance gain.I took mine off,March pullies.There for sale if you want em!!CarFreakGT said:
I really felt the difference, some don't for some reason. I had the ASP Street series. Maby the motor got a little warmer at idle, charged not quite as well, but after the 3G alternator swap, that fixed that. Did an electric fan too. A/C and smog was then deleted. Since then I have become an underdrive fanatic, I went and got the 3" crank pulley, I could read the belt numbers whith the car at idle, made a noticable difference. Didn't start to charge until 1600rpm but it's not a daily driver, and I have a good, oversized battery in the trunk. Now the only accesorie I will have is the alternator. (manual rack, electric W/P) A deep cycle battery is also a good idea when you really get serious.
I noticed the power increase right away. Basically, quicker response when you mash down the throttle.
My alt is old, as is my battery, so I went back to the stock alt pulley and went with a different belt size. From stock to underdrives, I maintained the same belt size without issue.
BTW - I am about to supercharge and have MAC pulleys with less than 7000 miles on them that I am looking to sell, so shoot me a PM with an offer if you decide to get some.
My alt is old, as is my battery, so I went back to the stock alt pulley and went with a different belt size. From stock to underdrives, I maintained the same belt size without issue.
BTW - I am about to supercharge and have MAC pulleys with less than 7000 miles on them that I am looking to sell, so shoot me a PM with an offer if you decide to get some.
willys1
Active Member
Michael Yount
Mustang Master
billybob - what's happened on someone else's car isn't predictive of what's gonna happen on yours. The pulleys include a smaller drive pulley on the crank which slows down all the accessories. Most street sets have an overdrive pulley for the water pump and alternator which speed those 2 back up -- but usually not as fast as they were spinning stock.
Some people experience problems - some don't. It depends on the car, how it's used, the shape it's in (cooling/charging systems) and geography. A lightweight, manual tranny, manual steering notch without a-c in rural Canada is less likely to have problems than an automatic, heavily optioned car with a/c and powersteering slugging it through stop and go traffic in Houston in August.
My car had ineffective a/c at idle, squealing power steering pump during low speed manuvers with the a/c on, cooling and charging issues at low speed. I removed the u/d's and put the stockers back on to solve the problems.
In my mind - for a race car, they should be standard equipment. For a race car that's just cruised from time to time on the streets, probably a 'yes'. For a street car/daily driver - I don't think they're worth the potential trouble they may cause. Especially when most of the power you may gain is gonna occur above 3500 rpm -- and most of the time on the street is spent below that rpm.
The only way to know what's gonna happen on yours is to try them. Save your old ones. If they don't work out, there seems to be an endless market to sell them used - just like the E cam.
Some people experience problems - some don't. It depends on the car, how it's used, the shape it's in (cooling/charging systems) and geography. A lightweight, manual tranny, manual steering notch without a-c in rural Canada is less likely to have problems than an automatic, heavily optioned car with a/c and powersteering slugging it through stop and go traffic in Houston in August.
My car had ineffective a/c at idle, squealing power steering pump during low speed manuvers with the a/c on, cooling and charging issues at low speed. I removed the u/d's and put the stockers back on to solve the problems.
In my mind - for a race car, they should be standard equipment. For a race car that's just cruised from time to time on the streets, probably a 'yes'. For a street car/daily driver - I don't think they're worth the potential trouble they may cause. Especially when most of the power you may gain is gonna occur above 3500 rpm -- and most of the time on the street is spent below that rpm.
The only way to know what's gonna happen on yours is to try them. Save your old ones. If they don't work out, there seems to be an endless market to sell them used - just like the E cam.
billyboy1955 said:
You won't have any problems or screw them up due to the pullies. Everytime you modify/change anything, you take a chance, but it is unlikley.
gruvee87vertgt
20+ Year Stangneter
I would recommend March or asp pullys...then throw on a 70 mm throttle bodie, msd coil and cap rotor etc...etc.
Yeah, don't worry about something getting "screwed up." The worst that happens is your battery does not charge well or your car runs warmer at idle. Then you sell your pulleys...or as in my case, you swap the alternator pulley back to stock. More power and better fuel economy are the common results of pulleys...more common than the problems, its just people tend to post about the problems far more than they do about the benefits.
Michael Yount
Mustang Master
....and the unaware have to be careful about swapping other pulleys on and off -- sometimes the results are unintended.
Most underdrive street sets have an alternator pulley that is actually an OVERDRIVE pulley -- smaller than stock -- to speed the alternator back up to some extent. If you take that one off, and put the larger stock one back on, you'll actually slow the alternator down even more exacerbating charging issues. Smaller drive pulleys (crank) slow EVERYTHING down. Smaller driven pulleys (water pump, alt) speed those accessories up. The amount of speed change is directly proportional to the ratio of the diameter of the pulleys being swapped.
The irony here is that MANY folks have added underdrives (about $40-100 depending on new, used, etc.). And then they spend another $300-$600 on 3G 130A alternators, aluminum radiators, electric fans/controllers to try and get the car to charge and cool properly. And, of course, adding the 130A alternator un-does the benefit of underdriving the stock alternator. So you end up spending $500+ for maybe 5HP most of which shows up over 3500 rpm.
I'm thinking that leaving the pulleys, alternator and cooling system stock, and throwing a 100-shot of nitrous on it would be a much better better performance improvement...
Oh - and the reason so many post about problems, is because they happen fairly often. The biggest culprit is charging issues. The stock fox body 65A alternator was marginal for meeting charging needs when the car was stock. Slow it down a bit - and it's an even bigger problem.
Most underdrive street sets have an alternator pulley that is actually an OVERDRIVE pulley -- smaller than stock -- to speed the alternator back up to some extent. If you take that one off, and put the larger stock one back on, you'll actually slow the alternator down even more exacerbating charging issues. Smaller drive pulleys (crank) slow EVERYTHING down. Smaller driven pulleys (water pump, alt) speed those accessories up. The amount of speed change is directly proportional to the ratio of the diameter of the pulleys being swapped.
The irony here is that MANY folks have added underdrives (about $40-100 depending on new, used, etc.). And then they spend another $300-$600 on 3G 130A alternators, aluminum radiators, electric fans/controllers to try and get the car to charge and cool properly. And, of course, adding the 130A alternator un-does the benefit of underdriving the stock alternator. So you end up spending $500+ for maybe 5HP most of which shows up over 3500 rpm.
I'm thinking that leaving the pulleys, alternator and cooling system stock, and throwing a 100-shot of nitrous on it would be a much better better performance improvement...
Oh - and the reason so many post about problems, is because they happen fairly often. The biggest culprit is charging issues. The stock fox body 65A alternator was marginal for meeting charging needs when the car was stock. Slow it down a bit - and it's an even bigger problem.
Michael Yount
Mustang Master
Oh - and Matt - if you like cars, there's going to be one heckuva car show April 1st down in Atlanta on Ga. Tech's campus -- the 3rd annual Ga. Tech car show. The turnout and diversity of cars is most impressive...
RUNINAGT
Member
Mine are aluminum pulleys from Mustangs Unlimited. I noticed a power increase in mine and I like'em. I put the stock alternator pulley back on because charging was lower then I liked. It brought it up some, and I was able to keep the stock belt. They have only been on for about 2mths maybe. I'll see what the long term does, but as of now they are staying on. Mine were $90.00 shipped.
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