Hey, I noticed my s5 alternator had a differnt plug than the s4 alterntor I have. Is it better in any way, or is the plug just differnt.

 

Its 10 more amps, 80 instead of the 70 of the 86-88. However, if you're gonna upgrade, just get the 100amp fd alt, it has the same plug as the 89-91, and if you have to modify the 86-88 anyways you may as well get the top line alternator.

 

how much modifying is there anyways? Just those 2 wires?

 

Snip off the plug and crimp on the newer one. Or just cut off the 86-88 plug and crimp on two spade connectors. Just make sure you pay attention to what wire is what. If you get them backwards, it will drain the battery.

 

If you're talking FD alternator, you need to swap the pulley and the shaft sizes aren't the same. You have to machine out the 2nd gen pulley, or buy a double pulley designed for the FD alt / 2nd gen swap.

 

Oh cool, maybe I will use my s5 alternator. do you know off the top of your head which wires to swap? I will need to ge a wiring diagram, but i'm too lazy for that

 

The FD Alternator isn't as easy as you make it sound...... You have to find just the right pulley for it. The FC pulley will not fit on it without some machining.

 

Im just going to use the s5 alternator actually for those 10 more amps! Oh yeah!

If I did get a fd alterntor, I would put it on a lathe, but I dont have the money right now and I have a spare s5 alternator laying around. Thanks

 

That's not how to do it. You can't just plug them straight in.

Alternator schematics: https://www.rx7club.com/attachment.p...hmentid=199213
Alternator pin-outs: https://www.rx7club.com/attachment.p...hmentid=170065

 

Thanks!

 

Oh really? Considering thats exactly what I did. As long as you use the right type of female spades they clip right in. Its been fine for 4 years.

 

whats the fd alternator charge at idle? mine is kinda low i think and at night time with lights on it drops down into 12s. its a rebuilt unit. is something wrong?

 

I am not sure about the FD alt but most modern small high output alt's use a delta wind rather than a Y wind
It is more efficient but is not as effective at charging at low rpm's
yours is probably normal

 

I didn't mean you physically couldn't, I meant you shouldn't because that's not the correct way for the alternator to be wired up. As you can see from my schematics, simply swapping the wires over doesn't connect it up as it's supposed to be. At best the alternator warning system will never work again. You may be happy with that, but I wouldn't be and don't recommend it.

 

ok im bumping this on one thing to be 200% sure the s terminal is the r terminal on the s4?

 

Just like it shows in the schematics above...