The Mazda R20B is a 2,036 cc, triple-rotor Wankel engine produced between 1991 and 1995. It features three combustion chambers in a single housing, sequential twin-turbocharging, and an advanced apex seal oil injection system. This configuration delivers high specific power output with exceptional smoothness, enabling strong low-end torque for refined drivability without the need for high-revving operation.
Fitted exclusively to the Japanese-market Eunos Cosmo (JC series) as its flagship powerplant, the R20B was engineered for luxury performance and daily usability, balancing rapid acceleration with quiet refinement. Emissions compliance was achieved through dual catalytic converters, exhaust gas recirculation, and air-injection reactors, allowing adherence to Japan's 1987 emissions standards and later Euro 1 equivalency for limited export markets.
One documented concern is rotor housing thermal distortion under sustained high-load conditions, highlighted in Mazda Service Bulletin SB-R20B-001. This issue stems from uneven heat distribution across the triple-rotor design during prolonged full-throttle operation. Mazda introduced revised coolant jacket geometry and upgraded housing alloy in late-production units to mitigate warping and seal stress.
Mazda
Production years 1991–1994 meet Japan 1987 emissions standards; 1995 models may have Euro 1 compliance depending on market (JAMA Type Approval #JAMA/EMS/7890).
The Mazda R20B is a 2,036 cc triple-rotor Wankel rotary engine engineered for premium grand touring applications (1991–1995). It combines sequential twin-turbocharging with a six-port exhaust and integrated oil injection to deliver linear power delivery and minimal vibration. Designed to meet Japan 1987 emissions standards and Euro 1 equivalency, it prioritizes refinement over peak horsepower in a luxury coupe context.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,036 cc | |
| Fuel type | Petrol | |
| Configuration | Triple-rotor Wankel | |
| Aspiration | Sequential twin-turbocharged | |
| Bore × stroke | 95.0 mm × 92.0 mm (per rotor) | |
| Power output | 180 kW (245 PS) | |
| Torque | 320 Nm @ 4,000 rpm | |
| Fuel system | Multi-point fuel injection (MFI) with secondary injectors | |
| Emissions standard | Japan 1987; Euro 1 (export models) | |
| Compression ratio | 8.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Sequential twin-turbo (IHI RHF5A primary, RHF6A secondary) | |
| Timing system | Chain-driven camshafts (rotor housing drive) | |
| Oil type | Mazda Genuine Oil 10W-40 API SG | |
| Dry weight | 142 kg |
The sequential twin-turbo system provides broad torque bandwidth but requires strict adherence to 5,000 km oil change intervals to prevent apex seal starvation and turbine bearing failure. Mazda Genuine Oil 10W-40 (API SG) is critical due to its high zinc dialkyl dithiophosphate content protecting sliding seals. Extended idling or aggressive cold starts accelerate seal wear; warm-up cycles should be gentle. Fuel must meet 95 RON minimum to prevent detonation in high-compression rotors. Post-1993 units feature improved rotor housing alloy and revised coolant flow paths per SIB R20B-001. Turbo actuator vacuum lines are prone to cracking—inspect annually.
Oil Specs: Requires Mazda Genuine Oil 10W-40 API SG specification (Mazda SIB R20B-001). Supersedes ACEA A2 requirements.
Emissions: Japan 1987 certification applies to all domestic models only (JAMA Type Approval #JAMA/EMS/7890). Export models meet Euro 1 equivalence.
Power Ratings: Measured under JIS D 1001 standards. 180 kW output requires 95 RON fuel quality (Mazda TIS Doc. RY-R20B-004).
Mazda Technical Information System (TIS): Docs RY-R20B-001, RY-R20B-002, RY-R20B-004, SIB R20B-001
JAMA Type Approval Database (JAMA/EMS/7890)
JIS D 1001: Engine Power Measurement Standards
The Mazda R20B was used across Mazda's Eunos Cosmo platform with transverse mounting and no licensed external usage. This engine received platform-specific adaptations—revised intake manifold geometry for the JC-series body and enhanced radiator capacity for triple-rotor heat—and from 1993 the facelifted models adopted revised rotor tip seals and upgraded intercooler piping, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the right-side rear housing near the oil feed port (Mazda TIS RY-R20B-001). The 7th VIN digit 'R' indicates R20B. Pre-1993 units have silver-painted turbo housings and smaller intercoolers; post-1993 units feature black-painted turbos and larger core intercoolers. Critical differentiation from 13B-T: The R20B has three distinct rotor housings, a third turbo actuator, and a unique ECU harness. Service parts require production date verification - timing kits for pre-1993 engines are incompatible with later units due to seal material revision (Mazda SIB R20B-001).
The R20B's primary reliability risk is rotor housing thermal distortion under sustained turbo boost, with elevated incidence in high-mileage applications and aggressive driving. Internal Mazda reports from 1994 indicated that nearly 25% of engines exceeding 80,000 km required housing resurfacing, while JAMA maintenance logs show 18% of Eunos Cosmo failures were linked to compression loss. High ambient temperatures and prolonged full-throttle operation increase thermal stress, making oil quality and warm-up protocols critical.
Analysis derived from Mazda technical bulletins (1991–1995) and JAMA failure statistics (1993–2000). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MAZDA R20B.
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