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Discussion Starter · #1 ·
Time has come to replace my alternator. There are a 90 and a 120 available. Price difference is nominal. Is there any reason why not to go with the 120?

Thanks in advance for your input.
 

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I suppose it depends on what vehicle you are installing it in. That extra 30 amps would come in handy for things like a winch, offroad lights, amp/subwoofer, etc. However, how old is your rig? The older, the better chance of watching your rig BBQ unless you do some electrical mods.
 

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Discussion Starter · #4 ·
J10Mike said:
I suppose it depends on what vehicle you are installing it in. That extra 30 amps would come in handy for things like a winch, offroad lights, amp/subwoofer, etc. However, how old is your rig? The older, the better chance of watching your rig BBQ unless you do some electrical mods.
'89 Dodge Ramcharger 2WD 360 CU 4 B Rochester Carb LE package. And Yes I do have a large Subwoofer that consumes a lot of current, but I do not want to see her "BBQ" it sounds you recomend to stay with the 90 amp.
 

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Discussion Starter · #5 ·
ram-it said:
One advantage would be more current at idle. A con would be need larger gauge wire than the 90. I would and did go 120
What did you update on the 120? Besides the alt to battery cable?
 

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Also note that depending on the year, the mounting brackets may be very different for a 90A and the optional 120A carb.  Some years the different amperage alternators were completely different designs.
 

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For 92, and 93, the 120 amp was standard for RC's, and window vans. I don't know if 89 was the same or not. Is there any numbers on your current alt?
 

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I've often wondered about the more amps at idle.  My truck came stock with a 60 amp.  I've put a EZ-EFI 1.0 with an in tank fuel pump, MSD streetfire ignition.  I've noticed that if I've go the lights and heater running I'm below down to 12.1 volts at the battery.  My car guy says I've got enough wire to go to 90 amp so I did.  No improvement.  However, at 800 rpm idle solves everything.  I can't decide if that's a high idle or not but I love the way truck runs with that idle set.  If I upgrade again, I'm going to go to a powermaster alternator 1 wire and just a new wire to the battery.  I've got an amateur radio habit though, so more is always better.  :)
 

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gremlinmt said:
I've often wondered about the more amps at idle. My truck came stock with a 60 amp. I've put a EZ-EFI 1.0 with an in tank fuel pump, MSD streetfire ignition. I've noticed that if I've go the lights and heater running I'm below down to 12.1 volts at the battery. My car guy says I've got enough wire to go to 90 amp so I did. No improvement. However, at 800 rpm idle solves everything. I can't decide if that's a high idle or not but I love the way truck runs with that idle set. If I upgrade again, I'm going to go to a powermaster alternator 1 wire and just a new wire to the battery. I've got an amateur radio habit though, so more is always better. :)
They vary a lot. It used to be the higher amp alts did have less output at idle. But nowdays, its all over the board. If you just need a little more RPM's to get the voltage up, I would look into getting a smaller pulley for the alternator. Since you are not likely racing with your truck, spinning the alt a little more will not hurt anything.
 

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FJBLF said:
What did you update on the 120? Besides the alt to battery cable?
Ammeter bypass, new voltage regulator (nothing wrong with the old one, I just like doing alts and regs as a pair due to a bad experience) and ground it. Also my install was on a bigblock so may not be applicable for you but I had to replace the top bolt with some redi-rod. With the BB there is not enough clearance between the head and back of the alternator to use the front most groove so I had to space the alt out from the head to use the rear most groove (I don't know if this is an issue with small blocks). So on top of the redi-rod I had to take some spacers from another truck and grind them down to fix the gaps.

Wasn't too difficult and completely fixed my headlights which used to dim at idle. Pretty sure I read somewhere that the Densos put out north of 40A at idle so its a no brainer if you have 60A. IMO there is absolutely no reason not to get a 120A over the 90. Cost is essentially the exact same for the upgrade and you get higher max and idle current.

Also not sure if there are any differences but if you search 91 Dakota Rockauto actually states which are Nippendenso units while searching 92 Ramcharger it doesn't, might be the same alts at the end of the day but I went with one that actually said ND.
 

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gremlinmt said:
I've often wondered about the more amps at idle. My truck came stock with a 60 amp. I've put a EZ-EFI 1.0 with an in tank fuel pump, MSD streetfire ignition. I've noticed that if I've go the lights and heater running I'm below down to 12.1 volts at the battery. My car guy says I've got enough wire to go to 90 amp so I did. No improvement. However, at 800 rpm idle solves everything. I can't decide if that's a high idle or not but I love the way truck runs with that idle set. If I upgrade again, I'm going to go to a powermaster alternator 1 wire and just a new wire to the battery. I've got an amateur radio habit though, so more is always better. :)
If you put in the 90A square back and not a ND unit it wouldn't really have had any better idle current than the 60A it replaced.
 

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No reason to do the ammeter bypass on an '80s or later model.  The shunt in the wiring prevents the issues the '70s era trucks have.
 

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amps/volts related but not the same . battery's can only handle so much amperage during charging , ideally you want your charge system to replace only as many amps as your using , plus a little to recharge after cranking . your voltage regulator should limit amount .  so , large alternators are good IF you have high current draw devices installed and in constant use , otherwise a waste ... their potential is never reached .
 
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