I agree with most of the above. The alternator only supplies what is needed, and the advantage to a higher amperage capable alternator is that it is CAPABLE of supplying more amps to the system if asked. The original alternator was sized in relation to the expected needs of the original car, and in theory, anything larger than that is not necessary.

But, if you go adding an electric fan on the radiator, fog lights, electric windows, a rear window blower defroster fan, or a huge bass thumping stereo system? You may need additional capacity. Contrary to opinions above, I don't think adding H4 headlights should be a significant change from the original system. You're replacing one high current draw item with another one of similar draw.

As for the wiring... since the alternator only supplies what is needed, if it's just an alternator capacity change and you don't add additional accessories, the wiring will not know that anything changed. But if you go adding those high draw accessories, you need to really study the current path(s) involved and make sure the wiring is up to the task.

I haven't looked, but I suspect availability could be an issue. In this day and age of more accessories is the norm and bigger is better, the higher capacity alternators may be cheaper and easier to find (up to a point).

I agree with most of the above. The alternator only supplies what is needed, and the advantage to a higher amperage capable alternator is that it is CAPABLE of supplying more amps to the system if asked. .........
But, if you go adding an electric fan on the radiator, fog lights, electric windows, a rear window blower defroster fan, or a huge bass thumping stereo system? You may need more........
As for the wiring... since the alternator only supplies what is needed, if it's just an alternator capacity change and you don't add additional accessories, the wiring will not know that anything changed.

A good Sgt always agrees with his Captain....

Will the larger alternator have more HP loss than the smaller alternator? I would think the armature(?) in the higher amp alternator would be heavier and slower to spool up plus when the amps get higher I would thing the HP loss would be correspondingly higher. I look at alternator amps sort of like I look at house electrical amps. You have a 200 amp house panel with 40 - 20 amp breakers in it; that's way more than the 200 amp service can realistically feed but how often do you have every branch circuit loaded to maximum? Ummmm, never...

In your Z how often will you have all the lights on, wipers on, heater fan on high, stereo kicking wide open, etc., almost never. Even if you did, the battery would supply excess power for a limited time then the alternator could replenish it when you cut some stuff back down. I can see a limited upgrade as potentially being good or going to an easier to source component but in the long run LED's would make a lot of this less necessary. Heater fan upgrade and fixing the wiper linkage would probably greatly reduce drawn amperage as well...

In theory, the larger armature would take more energy to rotate because of the mass, but I bet the difference would be so small that it would be negligible. Some tiny fraction of a horsepower. In other words, I believe the difference between a 100A capable alternator being asked to deliver 30A is going to be almost identical to a 40A capable device being asked to deliver the same 30A.

Now about the other part... Yes, the more amps you ask it to put out, the harder it will be to turn. So a 100A alternator delivering full rating will certainly take more power to spin than a smaller one being asked to deliver it's full rating. Haha! Did I say that right?

3 hours ago, Patcon said:

In your Z how often will you have all the lights on, wipers on, heater fan on high, stereo kicking wide open, etc.

Only every time I'm driving at night in the rain and a good song comes on the radio.    Oh wait... I'm not out in the rain?

You can mount a smaller pulley to "overdrive" an alternator too. But most higher amp alternators are just the result of better manufacturing tolerances and advanced coatings on the windings. More windings equals more current. Therefore a newer alternator will always default larger due to improvements in manufacturing and technology.
Again think of it like a memory stick. 8mb cards were the standard in the 90's, 128gb cards are standard and use the same space on the logic board. Why build 8's when you can make a card 100's of times more powerful for the same cost or less??
Hence larger modern alternators. At some point though, the vehicles draw is considered and there is no point in building them bigger. On our old Z's, with a few modern upgrades etc, I think a 100A alternator should be just fine.

Good point. I also wouldn't be surprised if there were other technological advances over the past forty years as well. More pure copper. CAD assistance for mag field design. More efficient internal regulators.

Okay, so what I'm getting from this is a headlight upgrade, fog lights, two USB plugs, the engine, the dash lights, the heater fan, seat heaters, and LED marker and tail lights, and the interior light *might* be too much for the ZX alternator upgrade and I should look into the capacity of my wiring harness.


But the one I started this thread with is probably overkill.

3 hours ago, Captain Obvious said:

Yes, the more amps you ask it to put out, the harder it will be to turn. So a 100A alternator delivering full rating will certainly take more power to spin than a smaller one being asked to deliver it's full rating. Haha! Did I say that right?

Dumb question, the force making it harder to turn would be magnetic force? I'm in grade 8 science class again.

Magnetic resistance. Negligible draw under normal load. Loss of hp would be too small to measure for most people. Plus if you are dead serious about power and performance, high electrical draw toys will not be on your build list...

My 370z for example, automatically kills the AC under WOT.... directs full hp to the wheels, not the AC pump!

4 hours ago, Matthew Abate said:

 I should look into the capacity of my wiring harness.

if the main wire feeding your fuseblock is too small, then yes. it doesnt matter how big the alternator is, if the wire is too small to carry the total load, you will have problems. you might think of adding a second fuse block that feeds the add-on goodies. also keep in mind that clean, tight, corrosion-free connections and grounds will help.

One of these is an awesome addition....