underdrive, overdrive??? for alternator

so i was reading something about using a chevy pulley to make the alternator spin faster so it puts out more juice at idle/lower rpm.

i can't remember/find where i read that. would i need a bigger or smaller pulley??? the rest i can figure out.

anybody got any specific applications that would work for the pulley???

larger pulley = your alternator turns slower
smaller pulley = your alternator turns faster

Hope that helps.

just did it to my 99. Works good, but I had to use microgauges to measure the original and then went to the JY and found one 3mm smaller which gave me about 5% overdrive.

These work for the old CS 130 (Renix) alternator http://www.alternatorparts.com/pulley_size.htm

They may be the same, they fit various manufacturers alternators, but a little more research for your 95 would be in order.
I went from a 2.25 inch to a 2 inch on my CS 130 (Renix) as close as I can figure it is about a 12.5% overdrive.

cool thanks.

any negative downsides to putting a smaller pulley on???

scorpio_vette said:

cool thanks.

any negative downsides to putting a smaller pulley on???

Click to expand...

Besides getting the old pulley off. which can be iffy even with a puller. I've heard a lot of horror stories, though I've been lucky so far.
Probably bearing wear and or extra heat.

Here is another interesting read. http://www.bc4x4.com/tech/2004/jeepalt/

Overdrive - may wear out bearings a bit faster (but we usually live at low RPM anyhow.) You'll get full output at a lower crankshaft speed, and you may increase total output of your alternator (but that is more determined by the voltage regulator and rectifier pack than by the pully size.) Will take more torque away from the rear wheels (just not sure how much) earlier in the power band if the electrical demands are high. Will spin your alternator fan slightly faster, allowing for more cooling at idle speeds (when alternator output should otherwise be low, reducing total stress on the solid-state electronics.)

Underdrive - will help improve bearing life slightly, but will lower the alternator potential output at various crankshaft speeds. Will reach full output at a higher crankshaft speed. Alternator will take slightly longer to cool at idle speeds when not at full output.

I would probably not suggest more than a 30% underdrive or a 12-15% overdrive for our alternators - more because of reliability concerns than for any reasons of output. Boy racers usually have component failures in town - we tend to have them about 100 miles from the nearest anything...

An extended idle switch that raises the idle speed when needed works for me. Police XJ's had them standard. Do a search and you'll find out how it works and how to install it.

can't do a hi idle switch on mine. that wire is not there and the port is actually capped of on my pcm. already looked into that. i do have a hand throttle that i use, but just figured i'd be nice to have the alternator working at lower RPM instead of having to hi idle it..............and because i can. LOL