to the OP
there is another thread that goes through the differences
The Carbonetics is a nice unit. Some (350Z's) have experienced issues with premature disk wearing, even using Carbonetics own fluid. I personally have never experienced it. The Carbon units they offer are not adjustable, so it does not allow for any customization now or down the road. That may or may not be an issue for you. They also require frequent fluid changes (every 3-5k miles) because the carbon dust from the disks contaminates the fluid. They are very smooth however and work well. You also are stuck using their fluid, so if you get it, stock up. We stock the diffs and the fluid BTW
Cusco - I've run one in my car since 2004 (I think...might be 2005!). It's a clutch type diff as well. It is adjustable from 1.5 to 2 way (2 way is for drift) and has 3 way adjustable lockup as well. With the right fluid, and the right setup (which IMHO is 60% lock, 1.5 way) it is nearly seemless. Mine makes zero noise. At a literal crawl at parking lot speeds you can slightly feel the inside wheel grabbing a touch...but you literally have to be crawling. At 5 mph, it's not present at all, for example. No special break in (no figure 8's needed!) and can use off the shelf fluid. Downside is there is a wait time for them (45-60 days at present). They are reasonably priced.
OS Giken - another clutch type diff, but has a bit of a different design. They are adjustable from OS Giken via diferent springs. Extremely careful tolerances means it is quiet and smooth. I've used them several times now on the 350Z's and they are unlike any clutch type LSD I've ever used. Higher cost vs the Cusco by a few bucks, but it's a drop in for base model cars on a 350Z (I'd have to check on the 370 base models).
Quiafe - top notch firm from the UK that has made diffs since forever. Theirs is a helical (gear) based unit. It is not adjustable at all, but it is literally so quiet and smooth, Nissan could have installed it from the factory and you would never thing it was aftermarket. A great street oriented unit. Works well for club type track days also, but not what I'd use on a full out race car.
Drexler - amazing unit but very spendy. Used by several high end OEM manufacturers, and many race teams worldwide
You can compare prices, specs, etc on our site if you like
Z-1 Performance Automotive Services Inc.
Given your conditions and needs/wants, I would select the OS Giken if this were my own car. My second choice would be Quaife.
