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Discussion Starter #1
Ray or anyone else , does the CS121 have a small dia case than the CS130 or is it just the stator dia ? I had an alt built a few years back and want to know what it was based on. I had first bought a CS130 but found out that the case was larger than the powermaster that i borrowed to build the billiet brackets and it would not clear the frame. I took it back and brought the power master with me this time. The guy said it was something that wasnt made for that long. He built me an alt with that case. Th one diff was it had a 3rd mounting tab on the case which I removed in the mill.
I am wondering what the alt was based on ?
or where there different size cases gor the cs130 ? I know I had thought it was the same alt as on my dads truck and looking at the powermaster in my hand and at the truck it seemed the same only to find out once he built one for me it wasnt
 

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The CS121 is 121mm around the stator, the CS130 is 130mm. That is only 9mm, but it many cases it is a big 9mm. The rear housings are maybe 2mm larger in diameter than the stator, really close to the same size. If you started out with a 3 ear housing, it had to be a CS121, here it is in stock form: http://search.waiglobal.com/partsearch/partnum.aspx?part=21-115 It is from a 2.0L GM 87-93. Now when I just went and found that in their system, they had crossed it to a CS130 replacement. Here is the front housing for it http://search.waiglobal.com/partnum.aspx?part=21-164-1 . So it does appear you could build a CS130 to replace your CS121. But you would need 1/4 to 1/2" extra room around the outside diameter of the alternator you have now.

CS121 advantage is weight, it is 2-3lbs lighter than a CS130.

Advantages to the CS130 is a lot larger bearings, about 40% bigger, which means better durability at higher rpm. And charge rates, the CS130 kicks the 121's butt.
 

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Discussion Starter #3
The CS121 is 121mm around the stator, the CS130 is 130mm. That is only 9mm, but it many cases it is a big 9mm. The rear housings are maybe 2mm larger in diameter than the stator, really close to the same size. If you started out with a 3 ear housing, it had to be a CS121, here it is in stock form: http://search.waiglobal.com/partsearch/partnum.aspx?part=21-115 It is from a 2.0L GM 87-93. Now when I just went and found that in their system, they had crossed it to a CS130 replacement. Here is the front housing for it http://search.waiglobal.com/partnum.aspx?part=21-164-1 . So it does appear you could build a CS130 to replace your CS121. But you would need 1/4 to 1/2" extra room around the outside diameter of the alternator you have now.

CS121 advantage is weight, it is 2-3lbs lighter than a CS130.

Advantages to the CS130 is a lot larger bearings, about 40% bigger, which means better durability at higher rpm. And charge rates, the CS130 kicks the 121's butt.
Yep that is what the front looked like. As i said we borrowed a powermater alt to build the brackets, its a low mount on a nova camaro, its located between the frame and block and once I went and looked at the truck i thought it was the same. I asked for a cs130 to be built with higher output only to find out it wasnt the same. I got the cs121 built due to the fact that I needed the size.

I have wondered for a long tiime now what it was after searching online tonight I figured I would ask
 

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Discussion Starter #4
BTW how much better is the charge rate of the 130 vrs a 121 ? and is this only in a stock alt or one that has been built for a purpose
 

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Stock a CS121 has about 50amps at 3000 rotor rpm and 74 to 80amps top end. I have built them to 134amps before and still had good bottom end (same as stock, it is hard to almost double the output and keep the idle charge)

Stock the CS130 has about 70amps at 3000 rotor rpm, and 105 top end. My lowest build unit is around 120amps at 3000rpm and 140+ amps in the top end. Same for our Thunder Series, but topend hits 160-180amp (sometimes 200). We also build them higher in the topend, 220+amps, and they are around 120 at 3000 rotor rpm (about 1000 engine), but at 800 engine they are just turning on. And we build a lower output unit, like 80amps max, but it turns on at 600 rotor rpm and maxs at 1800-2000 rotor rpm. Used for low rpm applications, like tractors, wind generation, etc.

The extra 2-3lbs of metal in the rotor and stator of the CS130 really make a huge difference in its output. The regulators, fans, pullies, brushes, and rectifiers interchange.
 
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