High voltage

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Holy Roller

Holy Roller

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If your running MSD ignition, what amp alternator would work? 60, 75 or 120 , it's a 383 in an a body. Thank you for your help
 
It depends on your overall load. "What else" you have hooked up. An MSD by itself is not a spectacular "draw." Also if you have factory stock wiring and ammeter, that is NOT gonna put up with something much over 50A especially after 50 years of nonsense
 
The MSD in and of itself isn't a huge draw but if your overall load (lights on, stereo blasting, etc.) and the load is more than your alternator can produce it would affect how well (or poor) the ignition system works.
 
67Dart273 said:
It depends on your overall load. "What else" you have hooked up. An MSD by itself is not a spectacular "draw." Also if you have factory stock wiring and ammeter, that is NOT gonna put up with something much over 50A especially after 50 years of nonsense
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Ok, all my wiring is new and if 60 amps is enough. Would that be a round or squareback alternator, the car is a 68 barracuda and the 383 came out of a 66 charger. The wiring was upgraded from small block to bb wiring harnesses.
 
70chall440 said:
The MSD in and of itself isn't a huge draw but if your overall load (lights on, stereo blasting, etc.) and the load is more than your alternator can produce it would affect how well (or poor) the ignition system works.
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Round or squareback?
 
The problem is if you are still using the factory TYPE wiring with the bulkhead connector and ammeter setup. Even "Ma" knew this was inadequate and on optional (factory) 65A alternators used what has become known as "police/fleet/ taxi" wiring. You can look that up in the shop manuals. They ran larger gauge wire through separate gromments through the firewall and bypassed part of the bulkhead connector. There are many many posts on that on this board. The largest type factory alternator in the original size case is about 65A. Squareback is generally considered a better deal. Otherwise you will have to adapt something else. Many on here have gone to a later style, and people like Mancini have brakets to support them
 
So is the car completely stock other than the MSD? As to which alternator, I believe there is a 60A in either version but I am not sure.
 
Think you'll need a 80 AMP alt like the 70's cars had with the electronic ignition, don't think the 60 will be enough, even going 100amp won't hurt anything but you'll have plenty of juice. Here's a calculator:
Calculate the Amperage You Need
 
Either actually I believe, both came in 60A or in some cases higher. I do know that you can get a round back from Power Master (Summit) that provides 98A.

That said, if your wiring is original, pushing 90A or more might (read will) create more problems, potentially a fire.
 
IIRC the MSD is an amp per 1K RPM. Did I read that somewhere? OOH, yes I did!

"...The amp draw is 1 amp per thousand RPM so at 4000 RPM, you should see a 4 amp draw at the battery." MSDtech
 
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70chall440 said:
Either actually I believe, both came in 60A or in some cases higher. I do know that you can get a round back from Power Master (Summit) that provides 98A.

That said, if your wiring is original, pushing 90A or more might (read will) create more problems, potentially a fire.
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You could get a JC Whitney winding that bumps the output of a stocker up about 50%.
 
70chall440 said:
So is the car completely stock other than the MSD? As to which alternator, I believe there is a 60A in either version but I am not sure.
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Pretty much, I may be upgrading the radio later. And may upgrade the headlights also, but other than that..nothing but the MSD
 
Well a 60A should get it done so long as the connections are good (like all of them especially the grounds). To that point, I would recommend you install some extra grounds, its the one thing Mopar did poorly (electrical system). I just finished completely rewiring my 73 Cuda, essentially building a custom wiring system and in doing so did tons of research on the subject as well as having 40+ years working on them. I can say with confidence that any vintage Mopar will benefit greatly from having good clean grounds and well as extra grounds installed (dash to firewall, engine to firewall and frame, etc). Time spent on this effort pays big dividends in the future.
 
There is a lot written on Mopar wiring and some dedicated websites, do some research yourself and you will be happy you did.
 
70chall440 said:
Well a 60A should get it done so long as the connections are good (like all of them especially the grounds). To that point, I would recommend you install some extra grounds, its the one thing Mopar did poorly (electrical system). I just finished completely rewiring my 73 Cuda, essentially building a custom wiring system and in doing so did tons of research on the subject as well as having 40+ years working on them. I can say with confidence that any vintage Mopar will benefit greatly from having good clean grounds and well as extra grounds installed (dash to firewall, engine to firewall and frame, etc). Time spent on this effort pays big dividends in the future.
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Sounds like a great idea, thank you for the information
 
 
 
Matts440 said:
Think you'll need a 80 AMP alt like the 70's cars had with the electronic ignition, don't think the 60 will be enough, even going 100amp won't hurt anything but you'll have plenty of juice. Here's a calculator:
Calculate the Amperage You Need
Click to expand...

70's cars DID NOT come with 80A alternator unless they were the large frame optional 105A setup which was HUGE. Saying "won't hurt anything" is uninformed. There are MANY cases of the stock bulkhead connector and ammeter failing with LESS than 70a alternators.
 
Holy Roller said:
If your running MSD ignition, what amp alternator would work? 60, 75 or 120 , it's a 383 in an a body. Thank you for your help
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Pretty much your stock alternator.
pishta said:
IIRC the MSD is an amp per 1K RPM. Did I read that somewhere? OOH, yes I did!

"...The amp draw is 1 amp per thousand RPM so at 4000 RPM, you should see a 4 amp draw at the battery." MSDtech
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Exactly.
The important thing is the main power wire to the MSD box (heavy red) gets a good connection into the power feeds. MSD recommends attachin git close to the battery positive. The only problem with that is when the engine is running, power will have to flow all the way from the alternator to that post. Its only a couple amps, so its not a big deal. At 6000 rpms you may see the ammeter indicate charge, because 6amps is going toward the battery. Really not a big deal. Don't like that, power it direct from the alternator.

Yes I've been running an MSD for something close around 80,000 miles with stock alternators, 37 amp to 60 amp.
 
In normal every day use, a high rated alternator would put out the same current as any other alternator.
There's two problems with high rated alternators( besides that some it is a marketting numbers game).
1. An alternator's rating is usually from its max output at higher rpms. Sometimes a higher max output is obtained at the expense of low rpm power output.
2. A high current demand situation is when a battery is run down. A discharged battery will initially suck a lot of current. If an alternator is capable of providing over 40 amps for recharging, that's way above what the wiring can handle. Its also not doing the battery any good.

Its really important to understand a few basic principles.
a. Power will come from which ever power source has the highest voltage.
b. Devices draw power.
- Alternator or battery only supplies as much power as demanded.
- Battery demand is a big variable. Generally its zero (fully charged). But when discharged it can draw a lot if allowed to.
Understanding Charging Systems with Ammeter
 
67Dart273 said:
70's cars DID NOT come with 80A alternator unless they were the large frame optional 105A setup which was HUGE. Saying "won't hurt anything" is uninformed. There are MANY cases of the stock bulkhead connector and ammeter failing with LESS than 70a alternators.
Click to expand...

Your right I stand corrected. Haven't had to deal with a stock bulk head for a while but never had a ammeter though, just the volt in my 72, my 67 has been completely rewired.
 
Mattax said:
In normal every day use, a high rated alternator would put out the same current as any other alternator.
Click to expand...

SORRY that is NOT TRUE. Yes, a higher rated output unit will put out the same as a lower one IF THE BATTERY is back up to normal and IF THE loads on it are "same as" a "normal car."

BUT all you need is A CIRCUMSTANCE

You leave the headlights on...........or play the stereo while parked.........or you flood it on a cold day and need a lot more starter cranking time

AND THEN the thing will output sky high amperage until the battery comes back up.

This is a well documented problem, folks. All you need to do is "throw" a nice big huge rated alternator on your stocker and if you did that to say, 100 cars, you would start to generate a pattern.......of failure........A few, even quite a few, might do "fine." I will guarantee you that others won't fare so well
 
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