Have a '91 NA coupe and am wondering what the differential is. It is an AT trans.

Is it a LSD or not?

How do I know or did all '91's come as LSD's?

 

According to Mazda, there was no LSD offerered in 91, other than on the turbo. There have been rumored to have been a few coupes that did in fact have the LSD, but it was probably just avery rare mix up, or leftovers being put in. Id say the chances of you having one are slim to none.
Alternatively, there is always the good burnout test. Put one wheel in grass (or any slippery surface) and the other on dry pavement, and try and spin the tires. If they both still spin (esp the one on the dry pavement) then it is an LSD.

 

the only S5 NA to come with the fabled LSD was the GTUs model.

 

Or you could just jack up the back of your car and have someone hold one wheel while you try to turn the other.

Although it would be a viscous, would that work

At any rate, if it is an open diff, the other wheel would just spin backwatrds as long as the car is in gear, while the rear end is on a jack.

 

Thanks for the help everyone. When on jack stands and turning one wheel, the other did go backwards.

 

I have an S5 NA. I have Viscous LSD. They are out there.

 

Well then your car is probably a GTUs.

 

Can't be. It has no rear wiper, and i think that the GTUs has engine speed sensitive stearing.
I can only assume that my car was purchased with from the factory with LSD. Or some random shizle like that.