ACT 1991 Mazda Miata HD/Race Rigid 4 Pad Clutch Kit
ACT ZM2-HDR4 is the dedicated race choice for a 1990-2005 NA or NB Mazda Miata: spec racers, time attack cars, and boosted track builds where a street clutch slips at the top of third or fades after a few hot laps. It pairs ACT's Heavy Duty pressure plate with a rigid, solid-hub 4-pad ceramic disc. ACT rates it at 310 ft-lb and recommends it for race use only, so it is not the kit for a car that sits in commuter traffic.
The Miata's clutch couples the four-cylinder's flywheel to the rear-drive manual gearbox. In ZM2-HDR4 the Heavy Duty diaphragm raises clamp load and resists deflection; ACT says each diaphragm goes through a four-stage heat treatment and the cover is a precision stamping for rigidity. The disc is 8.8 in (224 mm) across, splined for the 0.9375 in input shaft, with four ceramic pads riveted to a heat-treated chromoly hub. Torque capacity is 310 ft-lb at the crank, which ACT puts at 74 percent above the stock clutch. The full kit weighs 11.0 lb.
Rigid means there are no damper springs in the hub. That saves rotating weight and lets the gearbox shift faster, and with only four pads the engagement is harsh and close to on or off. ACT is clear about the trade: more gear rattle at idle and low speed, and the rigid design may increase spline wear on the disc and input shaft. ACT rates pedal effort as light to moderate, so the pedal itself is not the problem; the bite and the noise are.
A true slip test is a full-throttle pull from low rpm in fourth gear with the engine warm. If the tach climbs faster than the car accelerates, the disc is not holding. Before you condemn the clutch, check the hydraulics: a leaking slave or tired master cylinder gives grinding into gears and a pedal that sticks or sinks, which feels like a clutch fault but is not. Our slipping diagnosis guide walks through the road test, and the shift flare versus slip guide helps you name what you feel. If the car mostly sees the street, look at the sprung ZM2-HDG4 4-pad kit instead; it has the same plate and torque rating but keeps damper springs in the hub.
Our listing title says 1991, but ACT lists ZM2-HDR4 for every 1990-1993 Miata with the 1.6L engine and every 1994-2005 Miata with the 1.8L, including the M Edition, LS, SE and 2004-2005 Mazdaspeed. It does not fit the 2006-and-later NC or the ND. The 1.6L cars left the factory with a smaller clutch than the 1.8L, so on a 1990-1993 car make sure the flywheel you run accepts this 224 mm clutch; ACT's lightweight flywheels for these cars are listed for use with the 1.8L clutch size. If your car has had an engine swap or an earlier aftermarket flywheel, send us the year and VIN, or compare the old disc diameter and spline count, before you order. Browse other clutch parts in the rebuild kits category.
| Brand | ACT |
| Part number | ZM2-HDR4 |
| Fits | ACT 1991 Mazda Miata HD/Race Rigid 4 Pad Clutch Kit |
| Vehicle fitment | Mazda Miata Hd/Race Rigid 4 (1991) |
| Type | Clutch Kits - Single |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Yes. ACT lists it for all 1994-2005 1.8L Miatas, including the Mazdaspeed, plus the 1990-1993 1.6L cars. It does not fit the NC or ND.
Both use the MZ012 Heavy Duty plate, a 4-pad ceramic disc and a 310 ft-lb rating. HDR4 has a rigid hub with no damper springs, which is lighter and shifts faster but adds gear rattle and may wear splines faster. HDG4 has a sprung hub that is quieter and easier on the driveline.
ACT recommends this kit for race use only. Expect abrupt engagement, chatter when easing away, and noticeable gear rattle. For a car that is driven daily, a sprung disc is the better choice.
No. The kit has the pressure plate, disc, release bearing, pilot bearing and alignment tool. Resurface your flywheel or replace it, and on a 1990-1993 1.6L car make sure the flywheel accepts the 224 mm 1.8L-size clutch.
Brake fluid. Use the DOT grade marked on your clutch reservoir cap and bleed the slave cylinder after the install.
