Ok I wanna overdrive the alt for a lil while till can buy or fab a brkt for my 140 amp alt.Do i wanna oversize the pully or undersize it.I remember seein this covered somewhere but after wastein 4 hrs lookin no luck findin it.

 

You want better charging capacity at idle? Then you undersize the alt pulley. Don't go too far down in size or you could risk bursting the alt if you rev the engine real high..

 

yea. Basicaly I just want ta put a bandaide on it till i can cather up the brkt i need to do this right.Is there much of a risk of burnin it out at interstate speeds as long as i don go to small??At an idle + that the local autozone/advance auto they have it readin 103-105 now.

 

running your alternator more than its supposed to is a good way to wear it out. alternators are designed to charge in a certain range even though they are rated at 105 amps or 140amps or whatever. think of it like running your engine at redline or near it ALL the time, you'll wear it out in a hurry. most alternators run on average at about 60-70% of their rating, and thats what keeps them happy. having a bad battery, changing the pully size, or disconnecting your battery with the engine running will almost always ruin the alternator.

 

Pulley size choice is always a compromise between charging capacity at idle and the safety/ longevity of the alt at high rpm's. Cranking up it's speed 20% may give it something like 50% more current capacity at idle, wear out the bearings & brushes 30% faster, and make it run cooler.. Don't worry about it wearing out, the same effect can be had by changing to steeper rear gears (without the benefit at idle) and you don't see people concerned about that.
What are those 103-105 numbers? Amps? If so that's a very high number already.. I don't see what should consume so much power that you'd need more..? Stereo? What voltages are you getting?

 

yea stereo/amp 12" woof/airhorns/upgrade to dual coolin fans/aftermarket fogs/occational cb with footwarmer attachment/and a few other nesesities.From what A-Z and such say alts chargin fine but at long lights and drive thrus with lights radio and heater/defroster blowin the in dash meter drops from 14 volts to like 10- and it actually affects the rpm to point where tach thats normaly pegged(STILL have to do the fix in this forum)drops to like 5k or 6k and i end up havin ta pop it into n to keep from stallin.Once i get back rollin everything comes right back up to norms .I know not to trust the fac gages but right now the seat of my pants and factory is all i have.I also understand that there maybe and are other issues but 1 the things i ALWAYS do to my new toys is upgrade the chargin system.So soon as can find the brkt the 140 amp drops in.Till then feel that slightly overdrivein the alt is a quick fix/bandaide.

 

Ok, all those extras really adds up so I understand you need to upgrade.. I think your dash meter is correct.. Do you feel that the low voltage make the ignition weaker causing the rpm's to drop further, or could the rpm's (& voltage) be dropping just because the engine is so heavily loaded by the alt.? Overdriving the alt could make the load issue worse. I was thinking if some kind of idle load compensating device could be of use to you. I have an old idea about a voltage sensing device cranking up the idle speed when needed. Anyway, when selecting a new alt you must be sure to compare the curves of the original vs the new ones, because some high amp alt's can actually have less capacity at idle than a smaller one.. Measure the circumference halfway around the pulleys with a tape on the outside of the belt. That way you get an idea of the rpm's involved.

 

np already checked the pullys they match perfectly.And heck if needed can swap em out.Shoot i have a few v belt alts here that can put this pully on just got lucky and ran across this one and at 11.00 couldn pass it up.as for the rpm drop it could be the rpms dropin due to load but the alt is stock for the car and belts not slippin so figure it's all the after market crap.

 

Heck the ac doesn't work right now and I never use it anyways.Thinkin of rippin the all out and runnin dual alts.time will tell .Time to take the son to his J.R.O.T.C. vetransday parade muster.I'm gone.