I couldn't find any direct info on this, so I decided to make it a direct query: Is it worthwhile or simple to upgrade the '74 era alternator with something newer/more powerful, or just stick with stock spec?

 

If you're needing a new alternator anyway why not get a bigger one just in case. I've recently upgraded mine from 78amps to 94amps (the biggest that will fit) in preparation for e-fans. The 78 *Might* do it, but the 94 definitely will.

As long as the physical dimensions are close (pulley must line up, mounting bolts etc.) it should be a straight across bolt-up change.
(';')

 

It serves no purpose whatsoever to fit a larger than stock alternator, assuming the output is adequate in the first place.

More powerful units are capable of overloading the stock wiring in extreme cases potentially leading to electrical fire.

 

The only wire at threat from a bigger alternator is the charging wire/ route back to the battery (maybe the earth strap if already dodgy) and should be evaluated/ changed/ supplemented.
The battery itself is capable of a lot more current than the alternator and everything is powered from the battery.
But I agree it generally serves no purpose provided the original is adequately specced. On some cars though, driving with the lights, wipers, rear screen heater, radio etc on can lead to the battery running down after a while in which case it may be a worthwhile upgrade.
The issue you are referring to is when loads of aftermarket "stuff" is added to the car without considering the wiring upgrades to go with it. Then the ignition wiring and associated wiring can be overloaded with disastrous consequences

 

I am using a Delco CS 130 in my Jag - no problem with the wiring being overloaded,...I am using it because that's what my 350 GM engine uses, which is in my car. One of the reasons GM uses this alternator is because a lot of cars nowadays, operate at lower engine speeds ( RPMS), this alternator is designed to produce strong charging capabilities at low RPM, so whether idling or driving along at low RPMs its still creating a good strong charge. I have the usual electrical equipment plus a bass amp, fog lamps, and a charger for my cell phone. I will soon be upgrading the headlights/dash lights.

 

My point exactly.

If no aftermarket stuff has been added, the additional capacity of the alternator has no benefit.

 

My experience is with Series III XJ6/12, not Series II.

That said....

The Series III XJ6s used (mostly) a Lucas alternator rated at about 65 amps. This was marginally adequate only in that it struggled to keep up with heavy loads as previously described- lights, wipers, blowers, rear window heat operating simultaneously. The voltmeter would drop-drop-drop at idle. If idled long enough the lights would dim and accessories slow down. In my experience this is an issue only in winter driving in stop-n-go traffic. Once the rear window heater is no longer needed the alternator can keep up with the other loads perfectly well.

I'm not personally aware of any cases of batteries going dead because of this but, if left at idle too long, with that combination of loads, it seems plausible.

If your alternator struggles the same way, and it concerns you, then an upgrade to a higher output unit might be in the cards.

I'd consider to be optional.

As an aside, many people place the blame on their favorite whipping post, poor old Joseph Lucas. In reality, the Lucas alternators are perfectly good ---as good as any other--- it's just that Jaguar under-specified just a bit. I'm sure Lucas would've been more than happy to oblige a request for more output....for a price.

Cheers
DD

 

Doug has it sorted.

UPGRADE your earths, engine, etc. If in doubt add a few more. That usually keeps the Prince of Darkness well at bay.

Any alternator is only as good as the earth circuit.

 

The rating of the charge wire/path is even more important.

If adding extra loads then the current and return paths need to be reviewed.

 

The original post inquired as to a higher output unit for the 4.2 XK engine. Options differ from those for SBC's.


But, the paths do cross. The popular Delco units can be installed on the
XK engine. I've read of two methods.


1. Swap out the air pump and fit the alternator there. Two, then??


2. Johnscars offers an adapter. This allows the Delco unit to reside where the Lucas unit left.


I agree with Doug. So longs as loads are moderate and the Lucas unit is in good shape all will be well. I've never had a need to engage the rear window screen heater. My Lump enjoys good grounds and a big 140 amp Delco. It's Cadillac donor had a lot of electric dodads.


Bigger alternators/generators have been a quest from way back.


In the early 30's cop cars got radios. Big drain along with sirens, lights, etc. Leece-Neville supplied a "high out put" unit for Ford V8's.


Much larger than the one nestled over the intake.
Cops liked them..


Carl

 

Oh, the rest of us got along with units that could get about 30 amps at most.


Carl

 

Almost unthinkable today with our rolling computer driven light show and entertainment centre cars, but true.

Corvettes of the '60s came with a 37 amp unit on non AC cars which worked just fine.

 

Before alternators most cars were fitted with dynamos!!

 

Dynamo aka generator???


And, before that, neither. A magneto did it!!
Lights and ignition.


Those before me, though!!


My first car, at age 16, was a 23 Ford T. Option battery and generator
ignition or magneto. Like most, the magnets in the mag were dud, and I ran it on battery plus generator. Rarely if eve, used the electric
starter. Cranked it with teen muscle or pushed it. Oh, and a tow from pal Billy's T for the first few efforts!!!


Carl

 

As do fire departments and ambulance fleets.

Leece-Neville continues to exist.

 

My God, you are old!!!! 2016 - 1923 + 16 = 109

 

Odd what numbers can be interpreted to mean???


Old, yeah, but not quite that old. Four score and six. Seven
coming up in September, I hope to still be here. Although,
on arising, it takes some doing to get the bones working.


Got that T in 46, I think. I was 16 years old. Car was 23 years
old. A lot of tales relate to it Another day or more....


And, yes, I've run across Leece-Neville in Google searches.


Carl

 

Guess that's why Grant thanked your post

 

13 months after upgrading to an 80 amp unit, no problems so far.(except the new one failed and was replaced by the supplier a couple of weeks after purchase)

https://www.jaguarforums.com/forum/x...-143721/page3/

 

I am puzzled by this thread. Not sure why fitting a decent alternator can ever be a negative thing.

At the end of the day I (Amps) = E (Volts) / Resistance(Ohms). If you dont have much in the way of accessory add ons , then you just have some head room, no more current is drawn.

If you do have a lot of accessories and they worked before , they arent going to draw any more current because you have a better alternator.

I like the idea of upgrading the main battery and earth cables, but I like that even if you dont upgrade you alternator. My main power cables are about twice as thick as stock battery cables (not my work BTW, but happy to see it there when I first saw it)

The only potential problem I can see is if you significantly upgrade the alternator and concurrently do some pretty mindless accessory upgrades.