C3 Alternator Question

[Tom R.]

My 78 calls for a 63 amp alternator, if its replaced with a 61 amp or high output unit, I'm curious:

What is difference between 63 amp and 61 amp?
What is difference between 63 amp and one with greater than 63 amp output?

I'm looking for a sub until my Pirkle prepared alternator arrives.

Thanks

[Jim T.]

Re: C3 Alternator Question

The difference between the 61 and 63 amp was no problem for my 70 back in 71. The alternator failed and under the the 5yr 50,000 mile warranty GM replaced my original 61 amp alternator with a later model 63 amp unit. I remember the service manager telling me I was getting a bigger output alternator than what originally came on my new car.

[Joe L.]

Re: C3 Alternator Question

Tom-----

There is, basically, no difference between a 61 amp and a 63 amp Delco-Remy SI-series alternator. For all practical purposes, they can be used interchangeably. I could never really understand why GM used these 2 different ratings. The internal and external parts were virtually the same.

For greater than 63 amps, which were originally used on some 79+ Corvettes, that's a different story. These units, which were rated at 70 amps, were Delco-Remy Series 15-SI. These alternators have a much larger case and internals than the 10-SI units.

[Jack H.]

Re: C3 Alternator Question

As others have mentioned, a 2-amp difference in peak output rating isn't going to amount to diddly in proper operation for your car. Also, if the replacement alternator has been through a rebuild cycle, you can't trust the current rating stamped on the case to actually indicate that alternator's peak current profile anymore!

What made different alternators have different current ratings was the combination of field winding coil and rotor used inside. So, the 'guts' of a given alternator may no longer agree with what's stamped on the case after a given unit has been re-built. If it generates more current than it did originally, FINE! The voltage regulator will simply respond by squelching current flow during battery re-charge faster/earlier....

The only way to truly know what you have with an alternator that's been through rebuild is put it on a test jig, spin it up to speed, call for max output and measure what it delivers. Most autoparts stores have alternator testers with varying degrees of sophistication with the lion's share capable of assessing peak current production.

[Greg A.]

Re: C3 Alternator Question

Tom,

I have a working alternator (not correct, but a replacement) that was on my '78 when I purchased it (I'm not sure if it's a 61 or 63 amp.) It has since been replaced with a correct dated model (not from John Pirkle but from Don ??? -- can't remember the last name, but he advertises in the Driveline). If you want to "borrow" my alternator for just the shipping cost (from Zip 97035), I'd be glad to send it to you.

Greg.

[Craig S.]

Re: C3 Alternator Question

Don Briggs....Craig