[FastBack71]

i am so confused what pullies DO?? it takes away all ur stuff?? if i got like steeda underdrive pullies what of my accesories would not work as well/at all.. what kind of gain are these things?

[SWEET2KSTANG]

you replace the crank pulley with a much smaller pulley to reduce rotating mass mass off the crank. the alternator and water pump pullies are larger to compensate for the smaller crank pulley. that allows for the W/P and alt. to turn at the rate that they are suppose to, not any faster or slower. there is a small gain off of them, usually around 8-10. i have the steeda UDP kit and all my accessories work fine. they are a good choice.

[acmillr]

I think you might have that a little confused...

The alternator and water pump pullies are larger so that they will turn slower. A larger driving gear (crankshaft gear) will make things spin faster. On the flip side, a smaller driving gear will make driven gears spin slower.
A larger driven gear will make the shaft that it is connected to turn slower, and a smaller driven gear will make the shaft turn faster.

Same principle as getting a smaller supercharger pulley will produce more boost because it spins the shaft faster.

So, underdrive pullies do just that. They underdrive your accessories (rotate them slower) to reduce parasitic loss on your engine.

[FastBack71]

so you loose some accesorie power? like.. watts on ur radio or power in ur ac?

[acmillr]

No, you won't lose anything.

[FLA Dreadhead]

im confused on that note as well....so you dont lose anything??
no delay when you change radio stations or nohing like that....
so there is no downside at all!!???
can it only help?

[SWEET2KSTANG]

i never lost anything, actually before the UDP's the battery light would flash on the insturment panel above 4800 but after the pulley change it quit. i have had the steeda UDP's for 2 years now without 1 problem.

[beheivjer]

There is a small chance of over heating and that should be it dc power loss would only show up if you had a monster stereo but who has one of them in a stang they weight too much. Ive never had a problem with them.

[ReverendDexter]

Might be covered, figured I'd chime in.

Underdrive pulleys are designed to reduce the rpm of your accessories relative to the rpm of your engine. This reduces the amount of parasitic drag they cause, but more importantly, it allows you to spin your motor faster without causing potential damage to certain parts. You don't want to spin your water pump so fast it starts cavitating.

The power gain is more of a side effect than a reason to go to them, though that doesn't seem to be the popular idea these days.

I would say if you're regularly hitting the high side of your rpm range, than get 'em. If not, don't worry about it.

[Invictus]

yup if you get them go with steedas though!!! the BBKS look cool but the design sucks!

[FLA Dreadhead]

oh allright so i get wut your saying, but wut im tryin to understand is how does my accessories have an rpm, this is new to me, i thought it just ran of the battery and the allternator....

and you say go with steedas, i wsa lookin at the roush ones, do you prefer the steedas over the roush ones?

[TheUNZippee!]

If say, you had a large stereo system as I do that draws a shitload of amperage, and you had it cranked up while sitting in stop and go traffic, you may run into some problems.But for regular driving, underdrive pullies will not affect the regular operation of your car at all.Besides, one can always go out and purchase a larger alternator. lol

Rick

[ReverendDexter]

Originally Posted by FLA Dreadhead oh allright so i get wut your saying, but wut im tryin to understand is how does my accessories have an rpm, this is new to me, i thought it just ran of the battery and the allternator....?

By accessories, we're meaning anything driven by the crank pulley. That means your alternator, water pump, A/C compressor, power steering pump, and supercharger if you've got one. Because they're hooked up to the crank via a belt, when the crank spins those accessories spin, and not necessarily at the same rpm as the crank (though at a fixed ratio, determined by the pulley sizes).

It's like a multispeed bicylcle. Your legs on the front cog represent the crank, the speed that you're turning represents your rpm, and the rpm of the rear wheel is your accessory rpm. Putting underdrive pulleys on is like putting that bike in a lower gear -- your still spininng your legs at the same speed, but your rear tire is going slower, which has the end result of making it easier to spin the pedals (i.e. more power). Now obviously, if you shift into too low of a gear, you're not going anywhere, which would be the danger of going to rediculously underdriven pullies (not a problem with anything you're gonna buy off the shelf). In other words, you wouldn't be spinning your alternator fast enough to charge the battery, the water pump fast enough to cool, etc, etc. Again, nothing that should be a problem with off the shelf parts.

Hope that helps!

[FLA Dreadhead]

yeah thanks, its a tad bit clearer to me now...so are there over drive pullies to make more power instead of underdrive?

[Invictus]

just get them, its an easy 2-3 HP and you will not notice a thing but every little bit counts in the end.

[StangAddiction]

Originally Posted by Invictus just get them, its an easy 2-3 HP and you will not notice a thing but every little bit counts in the end.

actually, at peak hp, they should make more like 5-8hp, and you wont notice it until then. Top of the rpm range that is, which makes sense...

[ReverendDexter]

Originally Posted by FLA Dreadhead yeah thanks, its a tad bit clearer to me now...so are there over drive pullies to make more power instead of underdrive?

No, overdrive pulleys would cost you power. Regarding my earlier example with the bike, it'd be like shifting into a higher gear. It's harder to spin the pedals, and every rotation spins the rear tire more than it did at the lower gear.

It's like putting your car in an overdrive gear... do you have more power or less? (I know, I know, power remains the same, you know what I'm talking about)

You'd go to overdrive pulleys if you were into rock crawling, or some other activity where you spend a lot of time at idle, and you need stuff to spin faster to work.

[TheUNZippee!]

They actually make overdrive pulleys? Not a sarcastic question, lol, I just don't know

[Trick Tuners]

Originally Posted by acmillr No, you won't lose anything.

Yes you will. Thats how they work. Weaker AC, weaker PS/PB, weaker alternator. UDP are for cars with very few bolt on parts that only want a little more power. Very few high powered cars run UDP. If you have a high hp car you want all the power you can get out of your alternator to run your high output fuel pumps, high # injectors, and possibly a high powered ignition.