1980 alternator 10SI or 12SI??

[theo law]

I'm after a definitive answer as to the correct alternator model number for my 1980 - is it a 10SI or a 12SI?

I know the correct part number is 1101075, and it's a 70 amp unit. As for the actual design number, I'm getting confused because several people have said several different things;

I have been told the following:

It's definitely NOT a 10SI, and should be a 12SI.

The 12SI began life in 1983, and is recognised by a plastic cooling fan, suggesting 12SI is wrong.

The 12SI began life in around 1977.

Clearly, none of these statements agree with the rest...
Would there be anyone out there kind enough to run thru the major differences between these two styles, and also tell me what I SHOULD have on the 1980?

If someone could put me in the direction of some good literature on the subject, I'm happy do my own reading! Would this be the kind of info to come from the Technical and Judging Guide? (Planning to buy this soon)

Thanks
Theo

[Joe L.]

Re: 1980 alternator 10SI or 12SI??

theo----

The GM #1101075 is a series 12SI alternator. The series 12 SI alternators are larger in physical size than the 10SI and that's the easiest way to tell them apart. 15SI are larger yet.

As a GENERAL rule, Delco internal regulator-type alternators for the 1969-85 period in the 37-61 amp range are series 10 SI, those in the 63-80 amp range are 12SI, and those above 80 amp are 15 SI. The 63 amp units can be either 10SI or 12SI, but most are 12 SI.

The 12 SI units were first used ABOUT 1977 or 1978 on Corvettes. Certainly, they were introduced way before 1983.