For Spec Miata racers running the original 1990-’93 car, there are few options available for a limited slip differential. The OEM viscous limited slip is one, but is difficult to find. So is the Mazda Competition Clutch Type, which hasn’t been produced in years. Updating to the 1.8-liter Torsen unit is an alternative, but the conversion adds 40lbs. and requires replacing the drive shaft and axles as well. Plus, it has higher friction and won’t operate if one wheel is in the air, as in heavy cornering or bouncing off a curb.
The best option may be the Cusco Clutch Type limited slip differential, which is a direct replacement for the open differential and fits in the factory housing, although new stub axles will be required. There is also a version for the current MX-5.
“There are a lot of people out there that still want a limited slip for their 1600 Miata,” says Steve Sanders, MAZDASPEED Motorsport Development Manager for Mazda North American Operations. “This is actually a better unit. It’s more tunable than the factory one. You can set the way it locks up, and you can change the bias.”
Adds Mike Allen, MAZDASPEED specialist: “It’s pretty easy to open it up and change the discs and the plates to come up with a different bias ratio. You can buy different cams to change your lockup. It’s important, because in Spec Miata, there are only a couple of options for the 1.6-liter Miata.”
Other parts may be needed, such as seals and bearings, to install the unit.
Click here for detailed technical information on the Cusco differentials.
MIATA / MX-5 CUSCO DIFFERENTIALS
| MODEL | YEARS | PART NUMBER | DESCRIPTION | NOTES |
|---|---|---|---|---|
| Miata | 1990-1993 | 0000-02-5500 | Cusco LSD 2-way; 45/45 | |
| Miata | 1990-1993 | T015-27-270 | Stub Axle – right | Stub axles are required if previous differential was an open-type non-viscous LSD. |
| Miata | 1990-1993 | T015-27-280 | Stub Axle – left | Stub axles are required if previous differential was an open-type non-viscous LSD. |
| MX5 | 2006-2013 | 0000-02-5501 | Cusco LSD 2-way; 45/45 |
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