the idea behind underdrive pullies is based on several factors:
1)on the belief by the gullible public that the factory engineers
really didn't understand what they were doing when they chose
the pulley size.
2)on the gullibility of the buying public that the pullies will actually
save them power by spinning SELF REGULATING engine mounted
accessories slower won't simply change the regulation strategy.
3)On the FALSE belief that the power savings quoted will occour
ANYWHERE except at the engines power peak rpm, somewhere that
most drivers never go.
4)And the belief that the advertising claims are actually based on anything except the belief by the manufacturers of such items that nobody will be able to prove their claimes are lies.
Advertising in essence is about turning half-truths into complete lies.
the Alternator often takes MORE power to turn at a lower rpm
once underdrive pullies are installed than it did before.
because the alternator is self regulating it will automatically increase the field current to maintain it's target voltage, the rub is that to create that voltage at a lower rpm requires more force to turn the alternator.
the faster you spin an alternator the MORE efficient it becomes and
the cooler it operates.
the PS pump isn't doing squat most of the time because there is a careefully
designed valving system...
the water pump? well mabey, other than on a dyno, if you spent an hour
at the HP peak rpm you'd see a difference.
considering the ability of a 4.0 to generate heat I certainly don't want
to spin my water pump any slower...
Particularly since when creeping around at low speed is when an engine
in a 4x4 really heats up... you LOSE all "ram air" effects of driving down
the freeway at 70mph....
And this allows for the fact that my primary use of 4x4 is
to AVOID going "offroad" and much of the rest is getting
back to a road if I'm not on one....
Or simply not getitng stuck on a sandfilled two track somewhere
on a Wyoming sageflat
AD