ok i could be wrong but from waht i understand a pullykit tends to make your car run a bit hotter due to the waterpump pully slowing down, the alternator pully slows down and releases horsepower but sucks if you need the juice to run an a.c. or nice stereo...crank pully not sure what the hell that does but if slowing down your alternator releases horsepower wouldnt putting in an alternator that gives out more juice give you horsepower? does that make sense?

 

I have the Steeda kit in my car.Most of the HP gain comes at high RPM's.The water pump moves enough coolant to keep the engine from overheating,I never saw any evidence of the engine running hotter.The alternator slows down but I never had any indication of undercharging,although I didn't use the underdrive alt.pulley.The crank pulley slows EVERYTHING down just by itself,alt,waterpump,a/c,powersteering pump,etc.But to keep things from slowing down too much you get bigger pulleys with the kit to install on the waterpump and alternator.The alternator only gives out as much juice as the electrical system will draw.Untill you draw more amperage than the alt.can send you won't have problems.One advantage of underdrive pulleys is all of the engine driven accessories will turn slower and therefore the bearings will last longer.I had 167,000 mi.on a Lincoln MK VIII with the original waterpump,a/c compressor,and p/s pump.The alt's were weak anyway.

 

NO, it does not make sense. any belt driven accessory driven by the crankshaft takes away some horsepower from the crank depending on how fast the device is being turned and what the output of the device is. if you use a higher output alternator, it will take more horsepower when it is putting out more amps under load than a stock alternator would. basically, the slower any accessory drives, the less power it takes to drive it. most underdrive kits work by using a smaller crank pulley which by itself would slow down the others but then they make the others bigger which slows them down even more and also allows you to re-use the existing stock belt as the length of the belt run is not changed when they resize the pulleys.