http://www.obxracingsports.com/performance.cfm?catid=3&subCatID=18&subCat2ID=2


Can someone explain how these bigger pulleys give you horsepower other than maybe being lighter. I'm not denying that they do, it's just that I don't understand how. I understand underdrive but not overdrive.
Also, has anyone usede these pulleys before? How do you like them?

basically, if you understand the concept of underdrive then u understand the concept of overdrive....Like the 5th gear in your manual tranny, or 4th in your auto, essentially, what it does is that for every revolution of the belt that would normally rotate the pulley one time, it instead only rotates the pully half way for example...This means that the pulley is rotating slower and thus consuming less power...Think of it this way...The belt speed is the same no matter what size the pulley is. If the pulley itself is bigger, then the circunfrence is larger and thus it would rotate slower for any given belt speed compared to a smaller pulley...hope this helps....Also, I have heard that most of the power gain is from the loss of weight and not the diameter change....
-Jza69

I'm not disagreeing with you, I am just still a little confused. So if your crank pulley is always the same speed, it just seems that either the 2 oversized pulleys would go against what the underdrive crank pulley is trying to accomplish,....Or the affect of the oversized pulleys would not revolve as much as the OE pulleys do and would not operate the altenater or PS pump as well. Neither one of these sound good to me.

So I'm obviously still missing the big picture if these increase your HP. But do you think these would give a noticable gain. If they give you more HP I would like to have them, but I just like to know how shit works before I use them. Thank for the good attemp anyway. I am pretty fucking stupid from time to time.:)

Hey, didn't someone buy these and said he was gonna give us the goods on how they worked? Whatever happend to that guy? Or did I just miss it? I don't know what the hell is going on anymore.

ill try to re -explain....a bigger pulley will rotate slower (lower RPM of the pulley), compared to a smaller pulley...This then slows down how fast the alternator etc. spins....A slower spinnning alternator consumes less engine power...the downside is of course that due to it spinning slower, its output isnt as great as it normally would be... This doesnt really effect a car unless your using alot of electrical power for example a heavy amplified system etc... As far as power gain, ive been told that its the best bolt on for our cars.. not including NOS of course. for myself, im saving up for that EVOVIII so i dont plan on putting any more hop up parts into my eclipse.

don't we have two power steering pulleys? or is one of those the ac?

I think he wants to know if having the AFX UDP and the OBX overdrive will work ok...since the udp is smaller, and the obx's are bigger....it seems they would cancel out..

The combo of a UDP and the over size pulleys will make them spin even slower.....

exactly...that combo would make the pulleys spin slowly giving you even more power...At some point, slowing the pulleys becomes a bad thing because your alternator isnt spinning fast enough....I am not too sure if its a good idea to use both kinds of pulleys at the same time....Sorry i cant help you with that one.

BRAINFART!

Ok. I think I got it now.
But now I'm wondering if adding these to the AFX UDP would be Ok and still power everything enough, to make it a worthwhile mod.
Whoever it was that put them on his car needs to shed some light on this subject and help us out here. I can't remember the guys name.
The fact that he never came back and gave us an update kinda scares me anyway. Thanx for all the help guys!:)