Average alternator efficiency is 50-60%.
An 80A alternator at 14.5 volts generates 1160 watts. At 55% efficiency, it takes 2100 watts to turn producing full power. One horsepower is "half a Columbus" of watts (1492/2=746 Watts/hp)
So, at max output, an 80A alternator draws 2100 Watts x (1hp/746 Watts) =
3hp
If you underdrive your pulley 2:1 instead of 4:1, you also require 2x the engine RPM to generate
any power at all.
If you stop reading right here it means all you'll gain from disconnecting the alternator completely is 3hp, and that's only if you're using 100% capacity, and you may compromise idle charging.
For more theory that's really not that important, it will draw 3hp ALWAYS at full load regardless of engine speed, as long as you are above the minimum and ramp up speed:
Here's an example graph of alternator RPM vs output. When the engine is off, field current is maxed out, trying to "spark" the alternator into producing more current, but zero hp input means zero watts output. As the alternator starts rotating, it starts generating power, while the field current stays maxed. Eventually, the speed is high enough that the alternator is producing maximum output, and any increase in speed means the regulator will decrease the field current to maintain proper voltage - otherwise you would overcharge your battery. Since the field current is decreasing as RPM increases, power generation remains constant, which means power drawn from the engine is constant.
So, the max you gain is 3hp, and ONLY if you need maximum alternator output to maintain battery voltage; the effect of underdriving your alternator by 2 versus 4 means you won't reach max power output of your alternator until the engine is at twice the RPM. But are you using full output of your alt? Most likely, no.
What happens to idle power generation? Suddenly it takes twice the RPM to generate
any power at all and you no longer charge the battery at idle - when you're in the pits, stuck in traffic at night in the rain with the wipers and defroster going, when you actually need the pulley speed.
So what about your water pump? How much power does it take? I haven't done a back to back comparison because I don't need an electric pump for the street, but a little online research tells me 2-4hp. But how long will you make that extra 3hp without any coolant left in the radiator? If you DO underdrive the waterpump, don't get a higher flow water pump - they actually flow worse near idle because the impeller is designed for high flow at higher RPM.
Also, if you drive the pump with a motor... where does that electrical power come from? Power usage reduction of an electric pump comes from it spinning a constant speed, because drag passes are short and you sit in the pits for a long time. The cooling system absorbs that heat and rejects it on the idle home. On the highway, where load is constant, suddenly you might find the electric pump can't keep up at 100% duty cycle.
Power steering? Well, who needs power steering anyways?
