I haven't seen this mentioned in previous threads, so thought I'd start a new thread about this specific point. To replace the 2G alternator in my '91 4.9 I've sourced a recently rebuilt 3G out of a 3.8 Windstar at the junkyard. And yes, I realize that I'll need to re-clock this alternator for use in the 4.9.

The one thing I've noticed is that the 3G has a larger pulley than the one currently on the 2G. Wondering if I should swap the smaller pulley from the 2G onto the 3G or just go with the larger pulley already in place? I imagine either will work, just wondering if the 3G likes to be turned at a different speed. Hmmm, does a larger pulley spin the shaft slower or faster??? Faster, right?

 

Larger pulley equals lesser revolutions per revolution of the motor

 

I didn't change the pulley on mine. Been running just fine for over a year now.

 

Figures, I had a 50/50 shot and got it wrong! Thanks for the correction.

 

Okay, that was my default decision, so probably what I'll stick with too.

 

The smaller pulley would be a better decision IF you spend lots of time idling with high electrical load... It would keep your power level up a little better.. If on the other hand you spend most of your time on the road at normal engine speeds the larger pulley will work fine...

 

A larger pulley will also drain less power from the engine, producing in turn less ampers at the same engine RPM than the smaller pulley would. Since you now have a 3G there is no need for the smaller pulley, it will produce more than the stock 2G at any engine RPM.