Would going from a 90 amp to a 120 amp nipendenso style externally regulated alternator produce more current at idle and low rpm’s? Or is the boost in amperage just at the rpm’s that produce near peak alternator output?

And a second question, at what engine rpm should an alternator like those mentioned be producing near peak power?

The associated wiring has already been upgraded, I would need to up the fuse on the alternator output lead.

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In the old days using the 100 amp did the trick full out at 900 rpm. Can not really help on new stuff

will still only produce how ever many amps is "demanded," even if you put a 200A alternator on. though I do remember the old 100A alternator of the 70s and 80s being said to put out more amps ("if system needs it") at lower RPM than the typical more common Mopar alternators of the time. If you have a 15A load on the system that is all the alternator will give you. no matter "which" alternator you use. I remember reading somewhere that all Mopars (except the "A" Bodies) with the rear window defogger grid got the 100A alternator. Even on an otherwise "bare bones" car. My 78 Fury is like this.

That said, I switched to a 100A on a 79 Ramcharger I had once. It was fine, until the 1st time I tried to "jump" somebody else with it, whose battery was deader than dead. The dead vehicle put heavy demand on my system, and the ammeter let its magic smoke out within the dash....since all of the current that came from teh alternator on that vintage Mopar ran it all thru the ammeter. vehicles that came from the factory with the heavy alternator, had some kind of "shunt" on the ammeter..... which my truck didn't have, because it wasn't a "factory" 100A equipped truck. and back then I did not know this.
In later years (your truck should be OK) I think they were all shunted.
When I put that HD alternator on the 79, I "thought it might be a good idea at the time" because I had it laying around with all of the required different bracketry between that unit and the "normal" Mopar alternators of the time, from a 75 Cordoba that I stripped out and junked.

I will add this..... I just completely went thru the wiring harness on my 85, I have the Bishko factory service manuals on CD, for both 84 and 85.... and I can remember from that wiring harness rebuild, that factory 100A equipped trucks had 6ga alternator wiring, "std" alternator equipped only had 10 ga "HOT" wire from the big lug on the alternator.
and I believe that "100A" alternator of the 70s actually "grew" internally to 117A in the 80s.... same alternator case.

when I redid my wiring on my 85, I left the factory wiring for the alternator in place, but I didnt like that they put all of what ever current requested from the alternator thru a blade/spade connector, at the back of the valve cover.... it's like a 8-way connector where the engine wiring joined the rest of the underhood wiring harness.
I left this intact plus I added another (redundant) 10 ga. that runs right from that same "HOT" lug on the alternator, straight to the "+" on the battery.
I did wire in a regular underhood fuse box like newer vehicles have to eliminate and replace my fusible links..... I did run this redundant 10ga thru its own fuse in the box.
the redundant alternator lead direct to the battery is something you might want to consider, should that heavier amp rated alternator ever has to produce more than your stock alternator was capable of......

those numbers shown in that page of the manual were the minimum amps you would look for, if you hooked up a VAT-40 type load tester to your car in order to test the alternator to see if it was "good" or not.

I used to run a 117 amp Lestek Marine Amp on my old 72 Dumpster. She had a sweet stereo system, and that alternator was excellent. @ idle, nothing slowed down, nothing dimmed, not wipers, lights, heater blower, nothing, I suspect my ignition system liked it as well, and that stereo just thumped with 2 10" running in open air.

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