Alternator options

I have decided to step away from carbs and put a Holley fuel injection kit in my Demon. I currently have a 451 and its in the car with AndyF's engine plate. I also have a powermaster alternator low mounted with his kit. I presume I'm at or close enough to the max output of that alt to exceed it with a FI setup. SO what options do I have? I would like to keep the alternator low mounted if possible preferably retaining Andy's low mount kit.

I bought and used a Powermaster 100 amp one wire GM style for my bracket car It is mounted down low on the passenger side of the motor plate.
What brand is yours ?

Don't change anything until you verify that you actually have a problem. Most OEM cars run just fine with 60 amp alternators and they have things like power seats, heated mirrors, climate control, etc. Once you have it running you can quickly verify with a clamp ammeter what the system draw is and then make a decision.

I’m in the midst of an alternator upgrade right now. At the advice of a racer buddy that owns an alternator shop, I’m going with a Denso alternator.

I use a Denso 60 amp alternator on the 512 EFI engine in my Duster. That engine has coil packs as well as EFI. The car has a big electric fuel pump as well as an electric fan for the trans cooler. It stays right at 14.5 volts at idle and while driving. Zero problems keeping up with the EFI system. I am going to put a 90 amp Denso in my Coronet but it doesn't really need it. I'm just putting it on the engine since I have it and I think it looks cool.

I have purchased and owned a lot of alternators over the years. I will say, do not believe everything they print in catalogues about their fancy alternators. Many manufacturers make claims that just aren't true....Had more than one argument with big name brand "Sales" artists...I won't bore you with all the details.....But I will give you a link to the best 1-wire alternators to date I have found:

https://www.cvfracing.com/search/searchresults/?search_query=alternator

If you want an alternator that can do double duty, and keep up with all the electrical load of dual fans, elec water pump, fuel pump and four head lights...Purchase one of their 140amp alternators....Hands down, charges at idle with a hell of a load on it....At 10 or 11 pounds, these kick but at low rpm compared to anything else I have run. Highly recommend them.

Following this thread as I also have a Holley Sniper and dual electric fans and I'm dropping below 12 volts at idle when the fans kick in with a 100 amp 1 wire alternator.

Which alternator did you choose from CVF? And would I need more than a 100 amp for electric fuel pump, Sniper, and dual electric fans?

After putting the Holley Sniper EFI on my boys Dart we used this 100 amp Power Master alt that's a one wire internal regulator and has ben working great on his car. I like that its a Chrysler alt and bolts right up with the factory mounting. Its been flawless on his car and I now have one on my 63. Ron

That doesn't surprise me. Check your alternator output with a clamp on ammeter and see what it is putting out at idle. I bet it isn't producing anything close to 100 amps at idle. Maybe only 20 or 30 amps. It isn't uncommon for one wire alternators to struggle at idle.

I have to get it up to about 1800 RPM's to get it back up 12.3 volts when the fans are running.

My new fans pull over 20 amps each + 8 amps for fuel pump + 1amp/1000rpm ignition + 8 amp water pump, plus 4 headlights pulling 5 amps each.....Still 13 volts at idle...A 100 amp was not doing it for me anymore, and I have tried all kinds of alternators on my cars.....These guys build an awesome 1-wire 140 amp alternator...

The Chrysler alternators, always blow apart on me, the chevy style ones are sometimes tough to excite them into working at low rpm, and then get enough amperage out of them.....Only brand I have not tried is the MSD one....

https://www.cvfracing.com/search/searchresults/?search_query=alternator

Here's another way I can put it.....How many batteries do you think I run in the car with a 605 Hemi that's almost 12:1 compression and all the electronics listed above plus Holley efi and a Pro-dash?

I run a GM CS130, they are supposed to be around 110amps. Runs all my stuff and has a rock steady output, the voltage lines on my data logs show almost no change.

You all need to understand that alternators ability to produce power increases dramatically from the 'turn on' rpm.
Whenever a manufacturer provides an amp 'rating' its almost always for an alternator spinning close at a speed it will produce maximum output.
There is no standard, so they can play various games with the 'ratings' and we have no way to compare.

A few things to check into.
Make sure the pulley ratio is spinning the alternator quick enough at idle.
Make sure the rotor has good wiring to it. A Chrysler roundback can pull from 2 to over 3 amps when full fielded. Some later Chrysler's pull 5 to 7 amps. Check the specs and make sure the wiring size and connections are adequate.

AC Delco used to have some graphics of the max outputs for some of the GM alternators
Shows the shape and gives a good comparison within the brand and product line.

Notice that is 'generator' shaft speed, not engine speed.
(GM didn't accept the term 'alternator' as it came from their competitors)
Also notice this graph indicates amperage at 14 Volts.
Chrysler shop manual tests were usually 15 Volts (tougher test) and many claims are made by using 12 Volts, which makes the output look higher.

I just installed a FAST XFI in my challenger and with dual electric fans and the draw from a good sized electric fuel pump the 60 amp alternator wasn't enough to charge at idle and low RPM. I wanted to try and maintain the stock look so I put in a Tuff Stuff 130 amp factory wire style externally regulated alternator. They say it should be good for 50% charging capacity at idle so being roughly double of what I had I figured it would be good. Well with both electric fans on it still drops to about 12.2 at idle and will jump up to 14.1 just off idle. I am now considering overdriving it a little more with a different pully arrangement.
AG.

Out of curiosity what is max RPM you want to spin an alternator?

Where are you measuring the RPM... at the alt or the crank
I have run my alt on the race car at 8500 crank rpm it has been to 9600 rpm,,
that is with a slightly under driven set up

At the alternator.

If you looked at the GM chart they show 12K at the gen/alt.. I know I use to test them at 10K+.. a ford
buddy use to blow up his alt at a much lower crank rpm.. he blew up 2 alts where the fields whould
come unglued but I dont know his ratio

That's a BS answer from Tuff Stuff.
They ought to be able to provide an output curve.
Unless they are just slapping parts in and have no test equipment. Lets hope not.

Changing components to produce a higher output can compromise the low rpm output.
This is another reason why the 'ratings' are somewhat useless for selecting an alternator.

This is from the sameAC Delco catalog that used to be on-line.


if your alternator is on the car, you can measure the output under various conditions using a DC inductive ammeter.
A Sun VAT40 is a good tool for that as it has a carbon pile, ammeter and voltmeter, etc. But a lot of modern multimeters and scopes also can be equiped with an inductive clamp for current measurement.
Without an external load, you can also measure the total load by turning everything on while running on battery. Put the clamp on the battery negative for that one. Keep the test short - 15 second is plenty.
On a classic setup, an alternator that could produce 5 amps more than the loads was considered OK.
But for a setup laden with critical high current electric needs (EFI, Fans, Pumps) that rule of thumb might run the alternator duty cycle higher than ideal. (ie it will run hotter than it should for long life). Someone else will have to advise on that.

Only Chrysler alternator performance curve I've seen is the one Nacho got in a box with a revised squareback ( IIRC).

https://board.moparts.org/ubbthread...stem-upgrades-73-e-body.html#Post2609330

Notice the test voltage was 13.2 V
So can't compare directly to test in the shop manual.
Assuming magnetic field is a strong as it can get, the we could calculate the power at 1250 engine rpm if we know the pulley ratio.
P = I x V
Then divide by 15 voltage to ge the current it probably would produce at the higher voltage.

I can tell you this about this one wire Power Master Mopar alt I am using on my 63. Its an internal reg of course since its one wire. The paper said it puts out 95 to 100 max and will put out 65 amps at idle. I had a stock 35 to 40 amp alt on my 63 and I added a single electric pusher fan in front of my rad I can turn on if stuck in traffic on hot days for a good bit. When I turn the fan on at night with the headlites on the volts drop from 14 to about 12.5 at idle. They go back to 14 at about 1500 to 1800 rpm when stepping on the gas. With the Power Master 95-100 amp one wire when I turn the fan on with the headlites on at idle the volts drops about a second to about 13 and then goes right back to 14 to 14.5 even at idle. But I don't run dual fans but I like that it keeps charging better at idle then the stock alt did. I never had any dead battery problems with the old setup but I like that this alt keeps the volts at 14 even at idle with everything on. For my setup and my sons with the Sniper EFI its worked great so far. Ron

My current alternator FYI


https://www.summitracing.com/parts/pwm-8172