Pretty Cool alternator swap

[J Series Trucks]

I just did a really cool alternator swap this weekend, so I had to share.

Most of our FSJs use Delco 10SI Alternators, the common small cased internally regulated
alternator that has the metal fan on it. My alt started squealing like hell when I was romping on it,
so I went to a U Pull It looking for some swap alternatives, and discovered that the Delco 12SI
alternator has the exact same dimensions as the 10SI, and is a direct bolt on.

The 12SI commonly comes in 78A, and is found on 80s GM vehicles. The case looks like the 10SI,
but the fan is a flat plastic part that has internal "turbo" fins on it-your pulley will swap onto it,
and if the only one you can find is not oriented the right way for mounting, you can separate the
case halves and rotate it, as I had to do to get it to fit the 455 Buick in my J Truck.

The 12SI put out better juice, and at lower RPMS!
Just some food for thought for you guys-I'm lovin it!

Brad Feick tongue.gif

[RWC]

I'm actually running a 94 amp; same deal. I can get a NAPA part number if anybody's interested.

RWC

[J Series Trucks]

Cool! You can also swap in the newer CS series, but I didn't feel like screwing around
with modifying my alt mounts-especially since it's a cast aluminum part on the non A/C
Buick 455s. When I eventually run the A/C on mine, the CS would be a big problem with
the stock alt/A/C mount anyway. Really happy with the 12SI!

Brad Feick

[TexasJ10]

How many amps is a 12SI?

[AzFrank aka Desertson]

A little FYI, I rebuilt my alt and used the parts,diod trio etc for a 80 amp alt. Mine before was a 63 amp.It cost only $20 in pasrt from AutoZone.

[PlumCrazyChris]

RWC, what is the Napa part # and if you remember, how much did it cost?

[Ralph]

I'm looking at another alternator, too, because I think my AutoZone-reman unit is giving me shaky voltage at low rpm's. I think this is affecting little things like my headlights and even my electric choke.

So, my question is: Does the 12si give stable voltage at low rpm's?