Someone here must know about the feasibility of swapping out the stock 70A alternator from the 1991 13B N/A and upgrading it to the one from the 1993- 9- Turbo 100A?
Someone here must have done this to eliminate the somewhat marginal performance of the stock 2nd. Gen. alternator.
Please list the pro's and con's. Fitment, fuse switch, etc.
What problems would I encounter or cause?
Suggestions?
As always, thank you.
Sincerely yours,
Robert

 

There's a few write ups in the archive as far as re-wire. and i think you may have to shim the pulley (?). but it's definitely a common swap.

 

Yep,

this swap is done all the time!

 

The FD alternator swap is almost "plug-n-play" for a 91 NA.

Your stock wiring will plug right in, you need not change the FD unit at all- it's the pulley that's different.
FD's use a serpentine belt instead of a v-belt and the shaft is slightly larger (@.060", IIRC).

After removing your old pulley you'll need to bore out the two pulley halves and the spacer to fit the new alternator's shaft.

The 100A's body is larger as well, you may need a slightly longer belt (I did) to give you adjustment room- I could get my old belt on but it was tight and the alternator was resting on the top of the shortblock. A new (stock) belt worked fine...I guess there are minor differences in length between manufacturers.

I replaced all the belts and the battery at the same time and my car was so happy that it started opening the sunroof sans nudging.
A coincidence? I think not.

 

Actually, there are differences in length even form the same batch of the same manufacturer. If you get two identical belts at the same shop at the same time, its almost guaranteed that one will be longer than the other.

 

Bringing back an old thread...

I'm in the process of doing this swap. The machine shop I took my dual pulley to botched the job and they are paying for a replacement. I'm just waiting for it to get here. While I'm waiting I was trying grind down the right size spacer and make sure the belts would line up.

Do you hapen to know what length belt you needed? I'm having the same problem with belts where I can't get mine around the pulley, my FD alternator has a rounded section on the frame that doesn't allow it to lower far enough to get the belts on. Thought I could save some guess work if you remember the length you needed

Just an FYI for anyone who's going to be doing this swap. I found the perfect diameter spacer at Lowe's. 3/4x1x1, obviously it's long, but the diameter fits very nicely.

 

I used the Gates Gatorback that is listed for the RX-7.
Apparently, different makers have a different idea of "stock" for the car but that belt worked fine.

 

2 belts from the same manufacture can vary in length.

 

for my spacer i went to pepboys and they took apart a couple old GM alternators, (just took off pulley) and after the 2nd shot we found one that worked, as far as the belt, i just used the stock belt that was on the car... i put it on like a bike chain as long as you are careful and pry in on nice and easy with a screwdriver while spinning other pulleys to get it to turn you should be able to get it on w/out tearing the belt, the nice thing is that its the back belt so if any other belts break you don't have to worry about off and on ...

also if you didn't get a pigtail with your FD alt, go to boneyard and most late model mazdas have the same alternator plug, hell its probably the same alternator too, i think i got the plug off of a 626 or something...

 

My belts are too short to even work them on. I can't walk them on, pry them on. With the FC alternator I could work them on, the one closest to the alternator being the hardest. But with the FD alternator on I can't get close to getting them on. With the FC I had plenty of room on the slider/tension side so I can go a little longer on the belt and still get the right amount of tension, I was just hoping to save myself trips and multiple purchases of belts.

I've got an S5 so the plugs are all good...it's just a matter of the spacer and belts...then I'll be good to go.

 

when ordering NEW belts......ask the salesmen to order from the same batch...IE: they have the same numbers on the belt.
and i THINK banzai makes a real nice pulley fit for this exact job.

 

I did this swap about 2 months ago and it went great! Took about 30 minutes total from removing the old alternator to starting the car with the FD alternator.

1) Dual Pulley...Banzai makes two...a "no frills" pulley that is like $20 and a super, nice, polished rotor shaped pulled for like $50.

2) FD Alt plugs directly into the S5 wiring harness.

3) You will need to do one of two things generally to get the pulley (Banzai at least) to sit correctly.
A) Machine down the lip of the Alternator.
B) Us a couple of oil cooler line washers as a spacer (Kevin Landers method).

4) I used two oem belts and it was tough but got both belts to fit.

Good luck!