The other day I was checking out my Summit magazine for headers when I ran across Underdrive pulleys. They were advertised to give you around 15hp and it was like 85 bucks. I was wondering if there really would be a difference or would I just be wasting money?

 

oh yeah there is a difference

 

I felt the difference. Never got the car on the dyno, but I felt the sotp more and more as the power was coming on. It free's up horsepower the engine already has which = more power to the rearwheels.

 

It's mostly SOTP hp that you get, on an LT1 really the only thing that the pulley runs is the water pump, which can be replaced with an electric one to free that up, then the alternator and the A/C compressor are only spun when needed, so in a racing situation you really won't make much of a difference, and in normal driving situations you can run into issues with low voltage because the alternator isn't spinning as fast as it needs to in order to power your headlights, radio and keep your car running. If I were you I'd invest in an electric water pump...

 

I fully agree. If you notice a power increase by going to underdrive pulleys on an LT1, it is just because of your imagination and wishful thinking. Do as 95slvrZ28 said, save your money and get an electric water pump.

 

seems like an electric water pump would be more, but I've never checked. But that would also make your alternator run more making the pully more useful. I wouldn't do the pulley either i don't think but for other reasons.