http://www.rotaryinnovation.com/new_products[1].htm

OK somone said that if you use a dual alternator pully that it is not good for street use because it is the wrong size, well wrong. If you click on the link they have one for $20 and it is the same as stock, but the only difference is it is dual, it is the one that is on my car. Also for deltron' why would you notice any power gain from an underdrive pully, it's not like it is pully 500 lb's of force.

 

I knew about the regular size one already. I think the underdrive pullys are not that good of an idea i don't race enough to warrent them.

 

The only time custom underdrive pully's are good is when you are racing and are usually at high RPM's so the underdrive pully's slow the other pully's down so there is not so much were. But when used on the street it will cause the alternator to not turn fast enogh, unless you just hot-rod the crap out of it. Anyways just use the stock underdrive pully's I think it is a waste of money to buy custom one's.

 

"Anyways just use the stock underdrive pully's "


Stock pullies are not underdrive pullies. They are normal pullies.

Underdrive pullies are designed to reduce the amount of parasitic drag placed on the engine. Running the water pump slower and the alternator slower allows more power to be used to turn the flywheel that much quicker. You will not see any noticable gains from just using one underdiven component. The set, as a whole, is only good for between 5-8hp.

You'd have to compare the stock crank pulley to the underdriven one to determine if they even reduced its size. Most of the sets I've seen leave the crank pulley at the stock diameter and simply increase the driven pulley to slow it down.