are pulleys good for adding horse power and if so by how much?

 

pulleys (along with belts) rob power and add weight to the front of the engine. most engines need them to run accessories. what are you really asking?

 

so its a bad thing? i was wondering if they added horsepower

 

I believe you mean power pulleys, in my expierence these are just another $100 gimmick that do nothing. I had these on my old '92 Z28 5.7L and put the stock ones back on, in the 1/4 mile and freeway driving they did squat!! Spent that money towards an exhaust system or something better.

 

The alternator, water pump, power steering pump are all driven by the pulleys off the crank...stealing a few hp. Aftermarket pulleys are designed to spin the accessories slower, reducing the amount of hp being stolen. That extra hp is now available to turn the rear wheels.

The problem is that spinning the accessories slower means they are doing less of what they do. The alt is generating less power, the water pump is moving less coolant, etc. TPI draws a lot of amps, unlike a carb, as does the in-tank fuel pump. Provide them less voltage/amperage and they don't work as designed.

Underdrive pulleys are OK for carbed engines which have a lower operating amperage budget, or race-only cars that run at high revs the majority of their service usage. A street car that has to idle at red lights, cruise at ~2000rpm, and whatnot is not a good platform for them.

 

I agree!