yes but the high rpm of our cars might cause the berings
in the alt to die fast just my .2 cents

 

As long as no other pulley sizes change, you are correct.

Think of it this way. You have 2 pulleys the same size connected by belt. Turn one and the other turns at the same speed right? Okay, make one half as big now. Turn the bigger one at the same speed, the small one will have to rotate twice for every single rotation of the bigger one. Sorry, if I had pics I'd show you, but your assumption is correct as long as you don't change the diam of the main (driving) pulley.

 

You are correct. For a given belt speed, a smaller pulley will make more revolutions than a big one. It could be expressed by a formula:

Belt Speed (divided by) Pulley Circuference = RPM

1000 ft/min (divided by) .785 ft/revolution = 1274 Revs/Minute

1000 ft/min (divided by) 1.047 ft/revolution = 955 Rev/min

.785 feet is the circumference of a three inch pulley
1.047 feet is the circuference of a four inch pulley

 

http://rx7cz.net/pics/pulleys/set2.jpg

is it jsut me or is that chair a t2 seat?

 

yes, it is TII seat

http://rx7cz.net/photos/rotary/

 

Sure a smaller pulley will spin the alt faster... that's why underdrive pullies are actually bigger than the origional ones. Underdrive is just that, the intention is to slow down the speed of the alternator to supposedly reduce parasitic drag. That's what all the companies advertise. The reality is that there is no real reason to change the speed. Most pullies are underdrive 15%. That isn't going to do a thing for the car except lower the electrical supply capabilities. The bearing will definately be just fine.

Same thing with main underdrive pullies, that supposedy slow down the water pump to reduce cavitation at hi RPM"S. The reality is that the definition of "high RPM's" in this case is *sustained* operation above 7k or 8k RPM's. Now, I hit that on a daily basis in my car... but it isn't sustained.

IMO, underdrive pullies should be reserved for strictly racing only where high RPM's are sustained... on a street car, it sure isn't going to gain you anything noticeable and if anything it could hurt you.