OS Giken MZ191-HCR Expanded Capacity Rear Diff Cover for 2016-2026 Mazda MX-5

Vehicle Fitment

• 2016-2026 Mazda MX-5 Miata (ND1 / ND2 / ND3) - 2.0L Skyactiv-G I4, All Trims (Sport, Club, Grand Touring), Soft Top and RF (Retractable Fastback)

Fitment Notes

• Fits all ND-generation MX-5 Miata models (2016-2026), including both Soft Top and RF body styles
• Compatible with the stock OEM rear differential and with OS Giken Super Lock LSD (MZ191-HA) - no additional clearance modifications required for OS Giken LSD installation
• Reuses factory drain/fill bolts and upper breather assembly from the OEM cover - no new hardware needed
• Factory fasteners are retained; dimensionally identical to OEM cover for precise fitment and retention of OEM side bearing tolerance
• Does not fit NC-generation (2006-2015) or earlier MX-5 models

Features

• Doubles the rear differential fluid capacity from 0.6L (OEM) to 1.2L, significantly extending oil change intervals under heavy track use
• Cast aluminum construction dissipates heat more effectively than the OEM cover, helping protect differential internals, bearings, and seals during sustained track abuse
• Two 3/8-NPT ports and one 1/8-NPT port enable installation of an external differential oil cooler and a temperature sensor for data acquisition
• Dimensionally identical to the OEM cover, maintaining factory side bearing tolerance for a precise, no-modification fit
• Direct-fit compatible with OS Giken Super Lock LSD - no additional clearance or machining needed

Specifications

• Part Number: MZ191-HCR
• Material: Cast Aluminum
• Expanded Fluid Capacity: 1.2L (vs. OEM 0.6L)
• Port Plugs Included: 2x 3/8-NPT, 1x 1/8-NPT
• Fitment: Mazda MX-5 ND (2016-2026) Rear Differential
• Hardware: Reuses OEM drain/fill bolts and breather assembly
• Manufactured: 100% in Japan by OS Giken

Included Components

• 1x OS Giken MZ191-HCR Expanded Capacity Rear Differential Cover
• 2x 3/8-NPT Port Plugs
• 1x 1/8-NPT Port Plug

Product Description

The OS Giken MZ191-HCR is a cast aluminum expanded capacity rear differential cover designed specifically for the Mazda MX-5 ND platform. The factory rear differential holds just 0.6L of fluid - a volume that OS Giken has found to be inadequate under sustained track use, leading to accelerated fluid degradation and more frequent service intervals. By effectively doubling the capacity to 1.2L, this cover dramatically extends the time between oil changes and helps maintain the long-term health of the differential internals, bearings, and seals under high-demand conditions.

Beyond the added fluid volume, the MZ191-HCR includes two 3/8-NPT ports and one 1/8-NPT port that enable connection to an external differential cooler and the installation of a temperature sensor for data logging - making it an essential upgrade for any track-focused ND build. The cover is dimensionally identical to the OEM unit, retains the factory side bearing tolerance, and reuses all stock fasteners and the upper breather assembly. It is also a direct-fit companion to the OS Giken MZ191-HA Super Lock LSD, requiring no additional clearance modifications.