Overdrive alternator pulley

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kennythewelder

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My alt is a cs130, I'm guessing. I know it's the OE alternator for a 97 Silverado. 105 amp. As for the pulley. By overdrive, what I mean is a smaller pulley to turn the alternator faster at idle. Summit shows a 49MM pulley as an overdrive pulley. The OE pulley is a good bit bigger. IDK maybe around 60MM maybe. Not sure, but bigger. So a smaller pulley will turn faster all of the time, and I know this, but it's at idle that I'm interested in. Even if it's only a few 100 RPM more, that would be a big help. At1000 RPMs and above, the 105 amp alt, has no issues keeping up. The big 3. ( or big 5 in my case, because I added extra ground wires) helped a lot, but it it's when your sitting at the red light, or getting some fast food at the drive through, where I see the alt gauge fall off. It helps a lot to just put the truck in P of N. That's why I figured a smaller pulley would fix the issue. Make the alt turn faster, and the issue should be fixed.
 

Supercharged111

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I just remembered something: I had an underdrive crank pulley before that included an overdrive alternator pulley. I got it used though, no idea what brand it was. You may start there with your search, trying to schmooze a supplier out of just the alternator pulley.
 

kennythewelder

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I just remembered something: I had an underdrive crank pulley before that included an overdrive alternator pulley. I got it used though, no idea what brand it was. You may start there with your search, trying to schmooze a supplier out of just the alternator pulley.
I see them as cheap as about $15, and as much as about $75. Just looking up info, it looks like the OE crank pulley is about 7.5 inches. The OE alt pulley is about 4.5 inches, so about a 2 to 1 ratio, give or take. And the overdrive pulleys run just under 2 inches. So with out doing all of the math, and taking a bunch of measurements, the 2 onch pulley should turn a little over twice as fast as the 4.5 inch pulley. Looking at 5he chart that @AuroraGirl posted, the OE pulley is turning around 1500 RPMs at idle of about 750 RPMs. The overdrive pulley should turn around twice as fast as the OE pulley, or around 3000 RPMs.
 

Dropped88

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Wouldn't a higher amperage alternator

I see them as cheap as about $15, and as much as about $75. Just looking up info, it looks like the OE crank pulley is about 7.5 inches. The OE alt pulley is about 4.5 inches, so about a 2 to 1 ratio, give or take. And the overdrive pulleys run just under 2 inches. So with out doing all of the math, and taking a bunch of measurements, the 2 onch pulley should turn a little over twice as fast as the 4.5 inch pulley. Looking at 5he chart that @AuroraGirl posted, the OE pulley is turning around 1500 RPMs at idle of about 750 RPMs. The overdrive pulley should turn around twice as fast as the OE pulley, or around 3000 RPMs.

Im actually going to pull a part tomorrow. And im thinking of snatching smaller pulley if i can find anything to do some testing on this. Is there any measurements you may like or any pulleys from some other manufacture for pic or measurement?
 

kennythewelder

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Im actually going to pull a part tomorrow. And im thinking of snatching smaller pulley if i can find anything to do some testing on this. Is there any measurements you may like or any pulleys from some other manufacture for pic or measurement?
Well, from what I've been looking at, all of the OE pulleys are close to the same size. All around 4 inches. The overdrive pulleys are about 2 inches. So a lot smaller. It also looks like smaller aftermarket pulleys will for Ford or GM.
 

df2x4

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Any way you can get an amp clamp around your fans and determine what they are pulling? This info may better guide you.

X2 on this.

Kenny, with everything running do you see around 14V on the gauge above 1K RPM? If not, your 105A stock alternator is probably being pushed beyond its limits. E-fan setups can draw a ton of amperage, especially when they first start up.

Hopefully you can get what you need with a different pulley, but if not you may need to look at higher output aftermarket alternators.
 
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kennythewelder

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X2 on this.

Kenny, do you see around 14V on the gauge above 1K RPM? If not, your 105A stock alternator is probably being pushed beyond its limits. E-fan setups can draw a ton of amperage, especially when they first start up.

Hopefully you can get what you need with a different pulley, but if not you may need to look at higher output aftermarket alternators.
Yes, I do see 14 volts on the gauge above 1000 RPMs. My thoughts are to try a smaller pulley first. If that doesn't do the trick, then I will eventually replace the alternator with a bigger or higher out put alternator. I have no issues with the battery keeping up with the extra draw, and that is why I have let this go so long. I just want to make it better that it is now, even though it's not a real problem. LOL, it's just triggers my little voice we all have, and that voice says, hey man, that just isn't rite. You need to fix that, before it's a problem.
 
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