im looking into a set of underdrive pulleys but i cant seem to find out how they actually work? how can replacing one circle with another circle free up 15 hp?????????

 

An underdrive pulley, which is a different sized, smaller crank pulley, reduces the amount that the accessories spin in comparison to the crank pulley. So if its a 25% underdrive pulley it will cause the accessories to spin 25% slower, freeing up power from their drag.

A search will pull up a ton more information than I can pull off hand. It will also show problems etc that people have had, along w/ gains etc...

 

ooo ok. so its basically just a different sized pulley................easy enough

 

They're a sales gimick. Nothing more.

That's just my opinion. The way I see it.... if you're driving the car on the street, why would you want to spin the water pump, the alternator, and the power steering pump SLOWER?

So your car gets hotter while sitting at a stop light?

So your alt is putting out even LESS amps than it normally does at idle while you're sitting there with your headlights and wipers on, the A/C cranked full blast, and got the stereo cranked?

So you have to put even more muscle into turning the car going through a parking lot at 1mph looking for a good spot?

All this so you can gain MAYBE 10HP at 5000 RPM???

That doesn't seem like a great way to spend ~$100.00 or more.

 

cool. pulleys are out!!! thanks guys

 

Yup... good for a strip-only car, but not always entirely practical for a street car. Especially not a daily driver.

 

Underdrive pulleys are good for a street car with a/c if you change the alternator pulley to the smaller one to retain the idle charging power. With the a/c compressor underdriven the head pressure stays lower at idle, the compressor cycles on and off less often, the clutch and compressor last longer, and you lose less power. The underdrive pulleys will give you somewhat better mileage and more power. I have underdrive pulleys on everything I have and like them. I don't believe that a car takes much muscle to turn anyway. I use underdrive pulleys even on my van. The power steering feels the same, just takes less tq, therefore less HP to turn. Turning a water pump a little slower won't hurt anything. It might open the thermostat a little more. Most camaros have electric fans so no problem there.

 

underdrives are wasted money for the street