S4 GXL Clutch type diff VS Miata Torsen diff in N/A S5
 

I got a 90 Vert and I am wanting to upgrade from my open diff, it's just a cruiser, nothing extreme I just wanna be able to do a nice burn out and kick it sideways every now and again.

I have heard that these two options are the cheapest effective way to go, any input viewers?

They both have their pros and cons. The Clutch type is better in every aspec, except it might need to have the clutches replaced at some point. The Torsen is great, but not as good for drifting as it needs some resistance to keep both wheels turning. If you have one wheel go off track the Torsen will turn into an open diff.

Don't the S4 units have a really low initial torque rating? Would it be advantageous to raise this?

In theory yes, but finding HD clutches to put in your 26+ year old differential may be a challenge.

I've been considering a few diff options for my car as well. I'd like to find a whole S5 TII swap ideally, at least in pieces over time.

Someone on here told me I could increase the initial torque rating up to 100 ft/lbs by shimming it. Is that a significant difference; I feel like there is substantially more torque applied to the gears in a diff than that, so much so that such a change wouldn't be very noticeable.

That is break away torque for the diff; not how much torque it can handle.

Break away, as in how much before it locks?

What do S5 GXLs come with in the rear?

Mazda has stock, and oversize discs, so you can set it to what ever you want

just an open diff, S5's are slightly decontented to make them cheaper to build. the ONLY S5's with an LSD were the turbo and GTUs