hi, i have the march serpentine setup for performance. the alt pulley is too big and doesnt spin fast enough at idle. is there a company out there that sells a smaller diameter alt pulley
thanks
steve

There are a dozen guys on this board including me running the March system with serpentine. Alternators are all working just fine with the size pulley in the kit. My guess is your '140 amp' alternator is at fault if its not keeping up with the electrical system at idle that you feel it should be doing. Maybe the internal regulator is bad on the unit. You should consider buying a 94 amp alternator from the local auto store and hook it up to see if it performs as you would expect. You can always return the unit for a full refund if it doesn't correct your problem.
Details on 10/12si alternators, amperage, and connector position are at
http://www.madelectrical.com/electricaltech/delcoremy.shtml

I run a Summit 12SI 100amp

12SI, 94 amp, at 3:00 (AC-DELCO # 321-266, Lester #7294-3)
Tell the auto parts counter person that “The alternator is for a 1984 High performance Chevy Camaro, with 5.0L (305G) engine, 94amp alternator

DURALAST 94 AMP DL7294 LLT $30.00 $69.99 - Autozone

If it is a 1 wire system it will not light up until 1200-1500 rpm, mine has also dropped out if the rpm stumbled too low for some reason.

the alternator is charging the battery fine. i tested with voltmeter and the battery has a cnstant charge of 14.4 volts .
i did however calculate the alternator rpm at idle 750 rpm with the march system and it was about 1250 rpm
then i calculated the idle rpm with the v-belt pulleys and it was 5215 rpm at 750 engine rpm..
when i adjust the carb to let the engine idle over 1000 rpm, everything is fine
so it has come down to alternator pulley diameter proof of performance tag states
output@idle---99 amps
output@highway speeds---146 amps
***output @ idle may be drastically reduced using power pulleys

Unless you spend hours at a time idling in traffic, I don't think you have a problem. My "original" 61 amp 10si don't charge much at idle either, down around 12 volts with the headlights on, and the voltmeter moves lower in time with the turn signals. It's the battery that was in the car when I bought it, no idea how old it is, six years plus, it's never gone dead or even cranked slow, not once.