6 cyl Alternator

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Fisher

Fisher

Old Guy with a Cool car.
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Can anyone tell me what i have for an alternator in my 71 Duster? What was the common amp size for that car. What will i need to run the car with a bigblock? I am running a chrome ignition box and a few aftermarket gauges. The battery will stay in the tray in the front of the car, not remoting it to the rear. I may change the headlights to a 55/65 low beam high beam combo too. What will the factory wiring accept, i dont want to cause a fire.
 
Yours is a duel field 67 amp. general alternator. Good enough for general use. Just check pulley alignment. Mopar alts. generally are just good enough but not great. Later models are better ( 97-105 amps.). My experience with Mopar ignitions is that the technology is 50 years old. I suggest MSD ready to run or Petronix thus eliminating the ballast resistor. This puts 12 volts to the coil all the time. Thus, a high output coil can be used. Same price, your choise. I don't like misfires
 
Is that an aftermarket/replacement unit? I thought they were only ever around 35 amps or something stock which is why you would likely have some damage to your firewall connector with the newer 70 amp alternators. I remember finding all kinds of stuff on the internet about bypassing the firewall connector to use modern day alternators.
 
NukeBass said:
Is that an aftermarket/replacement unit? I thought they were only ever around 35 amps or something stock which is why you would likely have some damage to your firewall connector with the newer 70 amp alternators. I remember finding all kinds of stuff on the internet about bypassing the firewall connector to use modern day alternators.
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old single field were 45, 70's dual field were 65 and you can get many denso's now over 100
 
I don't know where you people get this stuff. VERY FEW Chrysler alternators were 65 A. Just because you had a "dual field" (correct term is "isolated field") does not mean it's high amperage. (I don't know what the smallest "squareback" was, 40? A)

The weak point is the bulkhead connector, ammeter. See this article

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

The PROBLEM is that rebuilders can rebuild just about any case into just about any amperage. So unless you KNOW you have an undisturbed original alternator, you don't know what amperage it actually is.

Worse, the rebuilders sometimes drill the case and put a non factory isolated brush holder in the older cases, so here's what the possibilities are:

Original pre 69 case, single insulated field connector

Modified pre 69 case by a rebuilder with added field connector

Early "roundback" 70 / later isolated field

Later "squareback" 73? later isolated field THESE ARE BETTER FOR LOW RPM

Below, on the left is a "round back" that is an oddball case. This alternator has a grounded brush (pre 70) installed at 9 o'clock, and an isolated brush at 12 o'clock, but a factory hole for an isolated brush at 3 o ' clock

The alternator on the right is a superior "squareback" which is what you should GET. Ask for a "mid seventies" alternator and do NOT accept a "roundback"

Unless you have, or plan to do the MAD ammeter bypass, I would not get more than about a 50A alternator.

squareroundcomp.jpg
 
THIS is the "rebuilder's hack" This is a pre-- 70 alternator which a rebuilder has drilled for an added, non factory, isolated brush. Not only do you get the older, inferior "roundback" and not only do you get a slipshod non factory brush, but if someone accidentally adds the original grounded brush, you can burn things up

128306-500-0.jpg
 
ok why would i need to bypass the amp meter on the car? Will it start a fire with an 80 amp onewire alternator? i am thinking that current draw is current draw, What is the max current that the factory amp meter can handle before it becomes and issue? i dont plan on having huge loads of current on this car.
 
There are no "6 cyl" alternators. Chrysler used the same alternator across all models at any time (pretty much). My 82 Aries alternator looked like the later "square-back" in 70's Darts.

Even the older round-back "single field" alternator (yours isn't) would work. I have kept that on my 65 Newport 383 w/ electronic ignition (XR700) and EFI (Holley Pro-jection) for decades, and my battery stays charged. Yours is an "isolated field" type (2 field terminals), but not the square-back case of later cars, so not sure the amp rating. However, it was wired in your car will still work. I am guessing you had the later electronic voltage regulator with the triangle connector. If not, perhaps one terminal was grounded.

Definitely use electronic ignition for the 440, unless really pinched for money. Hard to beat the $59 new HEI distributor on ebay for RB engines. At least look at it.
 
Fisher said:
ok why would i need to bypass the amp meter on the car? Will it start a fire with an 80 amp onewire alternator? i am thinking that current draw is current draw, What is the max current that the factory amp meter can handle before it becomes and issue? i dont plan on having huge loads of current on this car.
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READ please the link I posted above to MAD electrical. It tells the story. The average "most of" these cars came with 40 some amps or less alternators.
 
Fisher said:
ok why would i need to bypass the amp meter on the car? Will it start a fire with an 80 amp onewire alternator? i am thinking that current draw is current draw, What is the max current that the factory amp meter can handle before it becomes and issue? i dont plan on having huge loads of current on this car.
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The dash ammeter pegs at ~50 A. However, before that your bulkhead connector can melt if the two main terminals (thick blk & red wires) have any more resistance than when it left the factory. Most melt, even with the standard alternator, unless 1963 & 1965 cars (A thru C body) which had a better design.

Read the many, many posts about bypassing the ammeter, replacing it with a voltmeter, or (if really smart) my design installing a "bypass diode" so your dash ammeter still works.
 
When switching from round to square, don't you need to change voltage regulators too? Ie from mech to electronic? I thought that.
 
pishta,

No such hard rule. Read post #6. If you view the link the OP posted in #2, you will see he has a round-back case with 2 "isolated field" terminals.

A few (squishy) rules:

You can wire a square-back alternator (isolated field) to work with the old mechanical regulator - just ground one terminal.

You cannot wire an early round-back to work with a newer electronic regulator (triangle connector), unless you change the grounded brush to an isolated one.

There are after-market electronic regulators that work with a "grounded brush" alternator. The main reason to use one is so you don't have to hack your car's harness.
 
Well, and not only that but the vast majority of parts store new replacement "early" (pre 70) regulators you buy are actually electronic nowadays, anyhow.

And that means that you can go the OTHER way. If you were in some geedunk town, and they had an early or even a Ferd regulator, you could ground one brush of your 70 and wire it up anyhow!!!
 
I ordered a complete front end kit from Source 440 they shipped me the dual field square back unit with the kit. So i gather thats the good one to get.
 
I know this thread is a few years old but when installing a duel field (square back) alt in a single field system does it matter what field you hook up to and what one you ground????
 
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The same question has been asked almost every week in the intervening 3.5 years and answer hasn't changed. "Dual-field" is a mis-leading term, all have a single field with 2 terminals. In early ones (round-back, but not all) a wire from the voltage regulator (Vreg) connects to one terminal and the other field terminal is grounded. In later alternators (square-back) both 2 terminals are isolated from ground, hence "isolated field" is the better description. One gets 12 V switched power, the other terminal goes to the later Vreg (triangle connector). Doesn't matter which terminal is which, other than perhaps to a pricky judge at a car show.
 
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