50 or 75 amp alt alternator ?

[boneheadsGeTeX]

I'm getting a alternator ,, but I realy don't know what's needed it a 70 gtx 440 it has electric fuel pump and msd ignition. Some stock. 50 amp cost 45 dollars then Iv seen 75 amp 150 dollars. Don't want to pay 100 more dollars of o do t have to.

 

[67 coronet]

always go the bigger one when you have custom electrical draw,ign and fuel pump are extra draw.50 amp is fine for all stock setup.

 

[boneheadsGeTeX]

Thanks. So I need more amps.150 dollar alternator not what I wanted to here

 

[hunt2elk]

If you go with the 75 amp unit, you will want to upgrade the wiring in your car.

 

[383man]

If you go with the 75 amp unit, you will want to upgrade the wiring in your car.

No he will not have to upgrade his wiring. The alt will only put out what the car demands. You could put a 500 amp alt and it will only put out what the car and battery needs as the regulator will control that. And the electric fuel pump and MSD is not enough to have to upgrade the whole wire harness. I have done that many times using the stock wiring. If you want to upgrade the alt output thats a good idea even with the original alt as is bypassing the amp gauge and putting a voltmeter in the car as thats a good idea. Ron

 

[hunt2elk]

No he will not have to upgrade his wiring. The alt will only put out what the car demands. You could put a 500 amp alt and it will only put out what the car and battery needs as the regulator will control that. And the electric fuel pump and MSD is not enough to have to upgrade the whole wire harness. I have done that many times using the stock wiring. If you want to upgrade the alt output tahst a good idea even with the original alt thats a good idea. Ron

Guess I should have said that I would upgrade the wiring to handle the 75 amps with a #8 wire and #12 fusible link from the alt. to starter relay and then probably do the MAD upgrade or Nachos parallel wiring if it was my car. But you are correct that he would not have to do any upgrades if he didn't want to. Maybe the OP is not familiar with the shortcomings of the electrical systems on our older Mopars.

 

[Michael789]

I just bought a 78 amp alt for 45 bucks at advance auto, core is 15.00 so 55 bucks with out the core. It's a rebuilt unit but if you're looking for a cheap route to go then this is it.

 

[nm9stheham]

It's not always true about an electronic ignition and fuel pump drawing a lot of juice. An MSD 6A draws 3.5 amps at 5000 rpm (.7A per 1000 rpm); that is not much more than a stock points ignition system at a couple of amps. A Holley 110 GPH pump draws 3.5 amps. The heater blower can draw 20-25 amps, and all highbeams on will draw 12-15 amps, not including tailights, dash light, etc.

So the only time the OP would be anywhere near in trouble with a 50A unit would be at night with the high beams on, pushing on the brakes, and with the heater blower going full speed.......and the battery wil supply the extra few amps anyway, just like in the old days. The lights will dim and the blower will slow some, but the ignition and fuel pump will just keep going.

 

[boneheadsGeTeX]

Thanks for the info, im doing the wiring when I complete the motor upgrades,, but if the stock 50 will work , sounds good to me , want be much driving at anyway,, thanks agin for the help,,,

 

[HawkRod]

So the only time the OP would be anywhere near in trouble with a 50A unit would be at night with the high beams on, pushing on the brakes, and with the heater blower going full speed.......and the battery wil supply the extra few amps anyway, just like in the old days. The lights will dim and the blower will slow some, but the ignition and fuel pump will just keep going.

The problem isn't with the max output of the alternator, but what it puts out at low RPM. At idle, the old alternators don't put out Sh** worth of current, so they will often not do well in extended idle/stop and go situations.

 

[383man]

Guess I should have said that I would upgrade the wiring to handle the 75 amps with a #8 wire and #12 fusible link from the alt. to starter relay and then probably do the MAD upgrade or Nachos parallel wiring if it was my car. But you are correct that he would not have to do any upgrades if he didn't want to. Maybe the OP is not familiar with the shortcomings of the electrical systems on our older Mopars.

I agree even with all the original parts on our old Mopars it wont hurt to upgade some of the wiring problems that are known. Thats why I bypassed my stock amp gauge as its 50 years old in my 63 all these years all the current for the car and battery go thru the amp gauge so I was getting worried it may give out one day and I bypassed it and added a voltmeter. The alt will supply what the cars needs to run everything and then just enough to keep the battery charged. If he had a real low battery and everything turned on like at night then the alt will put out its most supplying the car and charging the battery. Once the battery has the proper voltage it will not take in much more (just a few amps to keep a good battery up) and then the voltage will be strong enough in the regulator winding to pull the contacts open and put the field thru a resistor or open circuit it to maintain the battery at the proper volts. If he had a bad battery that kept taking in current but would not charge up then the alt would put out more for longer then normal. But in normal conditions it will only put out no more then the older smaller alt if it was up to the cars demands. Good luck with it. Ron

 

[Nacho-RT74]

I just bought a 78 amp alt for 45 bucks at advance auto, core is 15.00 so 55 bucks with out the core. It's a rebuilt unit but if you're looking for a cheap route to go then this is it.

totally agreed. No need to pay those overpriced pieces. UNLESS they guaratee to put out more than 55 amps iddling. Stock 78 alts ( earliers 80s Mopars ) gives 45-48 amps iddiling, with the smaller pulley.

You need the more output as posible IDDLING... doesn't matter the max output, as far you fill the car requirements iddling

 

[nm9stheham]

The problem isn't with the max output of the alternator, but what it puts out at low RPM. At idle, the old alternators don't put out Sh** worth of current, so they will often not do well in extended idle/stop and go situations.

My point is that the MSD and fuel pump will not crap out at idle even with low alternator output at idle; those are a few added amps, and the load pales compared to blower and lights load. The battery will supply the extra needed current at idle and then get recharged when cruising. It DOES make the battery and its connections being in good condition more crtical, however. The older systems utilized the battery to take part of the load at times a lot more than newer ones.

 

[Nacho-RT74]

yes, but no nm9stheham!!

if you hook ANYTHING to the batt, you are adding an unnecesary load and stress through bulkhead and ammeter. This has being the BIG mistake FOR YEARS everywhere in the world on a full load ammeter cars when adding extra equippments, which adds more fails to the wrong alt amp rates used by Chrysler from factory

with the propper alternator, this stress won't be ever running throught ammeter and bulkhead connectors being correctly sourced from alternator or an splice or juntion box/stud between alt and ammeter into engine bay.

 

[nm9stheham]

Well, I cannot see the difference between running a few amps load via the battery bulkhead connector versus the alternator bulkhead connector; they are the same connector. If you have an an extra, large load sourced direct from the alternator, then it does as you say. But you're kinda mixing questions, IMO; you're getting into the where to hook up these accessories.

And anyone who thinks an added 10% load will do anything bad is not thinking. An added 10% load ain't going to cause a car to burn up; an added 50% load IS an issue. One thing that everyone else is missing here is that the MSD current draw goes down in proprotion to RPM. The old points system does not; it stays steady at several amps at all RPM's (as long as the points do not start floating at high RPM's). So the MSD will not be drawing much at idle RPM anyway. And nor will the fuel pump as it's fuel load goes to almost nil at idle.

With the orignal alternator with the original lights and blower loads, lots of extra currrent will need to come from the battery when the alternator is sagging at idle. Adding a few more amps will not make the car fail; address the actual loads that the OP is listing, not some general case of a mega stereo, etc. I would not say this for someone listing a ton of new loads.

Of sourse this is all a moot point if the OP decides that a cheaper rebuilt 75A is the way to go; problem solved...... 'til he is told agian that the wiring won't take the load and we start all over again.

 

[HawkRod]

My point is that the MSD and fuel pump will not crap out at idle even with low alternator output at idle; those are a few added amps, and the load pales compared to blower and lights load. The battery will supply the extra needed current at idle and then get recharged when cruising. It DOES make the battery and its connections being in good condition more crtical, however. The older systems utilized the battery to take part of the load at times a lot more than newer ones.

I don't disagree. But the key point in my post was "...they will often not do well in extended idle/stop and go situations." That is precisely for the reason you stated: at idle the battery is then supplying the extra current. It can do so for a short while, but the longer it does so, the weaker it gets. Also, the lights will dim a bit since they aren't as bright at 12.x volts vs. nearer 14. That happens even with a good battery.

For me, I would prefer to minimize that issue and get an alternator that can supply greater current at low speeds.

The total load the wiring can handle is a whole other subject. As people have stated, the wiring needs are dependent on the maximum electrical draw that the system will pull, it doesn't matter how much the alternator puts out...

 

[Nacho-RT74]

Well, I cannot see the difference between running a few amps load via the battery bulkhead connector versus the alternator bulkhead connector; they are the same connector.

same kind of connector, but diff side of ammeter so you can affect both or just one side. Depending on Alternator and Battery capacity

Of course, with a more powerfull alt and sourcing correctly, basically will be affecting just alt side of bulkhead. So a Bypass through the firewall is recommended. But since you are making this job, then make it on both sides at the same time, to a healthy charge and discharge circuit keeping safe the bulkhead (where all loads begin to burn everything )

- - - Updated - - -

...That happens even with a good battery.

For me, I would prefer to minimize that issue and get an alternator that can supply greater current at low speeds.

The total load the wiring can handle is a whole other subject. As people have stated, the wiring needs are dependent on the maximum electrical draw that the system will pull, it doesn't matter how much the alternator puts out...

totally agree...