underdrive pulley


Carz 'N Guitarz
everyone keeps talking about getting an underdrive pulley....what is it...and what does it do??? how much $ ?



Another Statistic
What do they do:
Pulleys are what powers the accessories of your car, power steering, air conditioner, water pump, ect. When you change the size of the pulleys you change the speed at which the accessories operate. A larger pulley will turn the accessories faster than a smaller one. The purpose of this is so that at idle for example, the alternator will turn at a high enough speed so that nothing is affected and your car has plenty of juice to operate all the power windows, locks, air and stereo. When you add an underdrive pulley you replace the larger crank pulley for a smaller one. Result, lower power for the accessories while at idle and a general slow down at cruising speed although not as noticeable. You'll notice the air may not be quite as cold. Or if you have a high end stereo system your voltage meter may read lower. Also the water pump is also slowed down. The point is to take power that the engine wastes on accessories and give some back to the rear wheels. It gives a general increase of anywhere from 5-10 HP.
How do they do it:
To give power wasted on the accessories such as alternator, power steering, etc. back to the rear wheels.


Another Statistic
Originally posted by SlowAsStock
The pulleys for your 2001 cost A LOT, simply cause they're newer and a new design or something. I believe they have your kind at www.rpm-mustangs.com look for bolt-ons.
This is where I have a set of ASP pulley's ordered.
Mikael is painting the Dampner since they always rust & look like crap. It will be gloss black the same color as the pulley.


Certified Auto Technician
"A larger pulley will turn the accessories faster than a smaller one. "
This statement is not true (I think he just typed it in worng), the larger the pulley is in diameter, the slower it runs whatever its attached to. Thats why Supercharger pulleys, the more power you want the smaller the pulleys. The U/D Pulleys and belts for my 94 are only $110, thats a smaller crank pulley and a larger alt pulley! Therefor, more revs, more power to the engine instead of the accessories, and a fact to note, is that all stock or OEM alternators are fully charged at around 950RPM, so if you run your vehicle below that range one-your an idiot, and two-you might (very slight chance) that your vehicle might die (T5s mostly, not autos I'm not sure?) Anyone who has already installed them, how many Dyno-horsies did you get?
A larger pully will turn accessories slower?? Uhh.. Depends on where the pulley is. A larger crank pulley will turn everything faster!
This is how it is. Since the crank pulley is the DRIVING pulley, a smaller one spins everythign slower. It is the exact opposite for the accesory pulleys since they are being driven, larger accessory pullies spin slower.

Blackhorse, i have the 01 pulley in belt in stock, email me for a price, [email protected]