The Mazda 20B-REW is a 1,963 cc, triple-rotor Wankel engine produced between 1989 and 1995. It features sequential twin-turbocharging, side exhaust ports, and an advanced apex seal design. This configuration delivers exceptionally smooth high-revving power with strong mid-range torque for everyday drivability.
Fitted exclusively to the Eunos Cosmo (JC) in Japan, the 20B-REW was engineered for refined performance and low emissions. Compliance with Japanese 1989 emissions standards was achieved through exhaust gas recirculation (EGR), a catalytic converter, and precise fuel injection control, allowing it to meet stringent regulatory requirements without compromising its rotary character.
One documented concern is premature rotor housing wear on early production units, highlighted in Mazda Service Bulletin M-SB-91-03. This issue stems from thermal stress cracking under sustained high-load operation, particularly when using lower-octane fuel. Mazda introduced revised housing metallurgy and improved coolant flow routing in mid-1991 production, resolving the problem in later units.
Mazda
Production years 1989–1991 meet Japanese 1989 emissions standards; 1992–1995 models may have enhanced compliance depending on market (JAMA Type Approval #JAMA/ENG/0112).
The Mazda 20B-REW is a 1,963 cc triple-rotor Wankel engine engineered for premium sports coupes (1989–1995). It combines sequential twin-turbocharging with side exhaust porting to deliver linear power delivery and high-revving character. Designed to meet Japanese 1989 emissions standards, it balances performance with operational refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,963 cc | |
| Fuel type | Petrol | |
| Configuration | Triple-rotor Wankel, side exhaust ports | |
| Aspiration | Sequential twin-turbocharged | |
| Bore × stroke | 95.0 mm × 92.0 mm (per rotor) | |
| Power output | 206 kW (280 PS) | |
| Torque | 370 Nm @ 4,000 rpm | |
| Fuel system | Multi-point fuel injection (MPI) | |
| Emissions standard | Japanese 1989 (later models meet enhanced standards) | |
| Compression ratio | 8.2:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Sequential twin-turbo (IHI RHF5A + RHF5B) | |
| Timing system | Timing belt (drives intake rotors) | |
| Oil type | Mazda Genuine Oil 10W-40 (API SG) | |
| Dry weight | 122 kg |
The sequential twin-turbo provides rapid response and sustained high-RPM power but demands strict adherence to 5,000 km oil change intervals to prevent apex seal degradation and turbo bearing failure. Mazda Genuine Oil 10W-40 (API SG) is critical due to its specific detergent package protecting rotor housings. Extended idling or aggressive cold starts increase risk of carbon buildup in side exhaust ports. The timing belt must be replaced every 40,000 km per Mazda SIB 91-01 to prevent catastrophic rotor misalignment. Turbocharger oil feed lines require inspection for coking; use only OEM gaskets during rebuilds. Early units (pre-1991) are susceptible to thermal stress cracking in rotor housings if operated below 98 RON fuel.
Oil Specs: Requires Mazda Genuine Oil 10W-40 (API SG) specification (Mazda SIB 91-01). ACEA A2/A3 oils are not approved.
Emissions: Japanese 1989 certification applies to all units (JAMA Type Approval #JAMA/ENG/0112). Post-1991 models feature minor EGR improvements.
Power Ratings: Measured under JIS D 1001 standards. Full 206 kW output requires premium unleaded fuel (RON 98) (Mazda TIS Doc. RE-105).
Mazda Technical Information System (TIS): Docs RE-104, RE-105, SIB 91-01
JAMA Type Approval Database (JAMA/ENG/0112)
JIS D 1001 Engine Power Certification Standards
The Mazda 20B-REW was used across Mazda's Eunos Cosmo (JC) platform with transverse mounting and proprietary licensing for limited export applications. This engine received platform-specific adaptations—reinforced crankcase ventilation and revised coolant routing—and from 1991 the facelifted Eunos Cosmo adopted the 20B-REW with improved turbo actuator calibration, creating interchange limits. No formal partnerships licensed this engine to other manufacturers. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the right-side housing near the oil filter mount (Mazda TIS RE-104). The 7th VIN digit indicates engine family ('B' for 20B series). Pre-1991 units have silver intercooler piping and single-stage wastegates; post-1991 units feature black-painted piping and dual-stage actuators. Critical differentiation from 13B-AP: The 20B-REW has three distinct rotors visible via the oil filler cap, with a unique intake manifold casting and larger turbo inlet diameter. Service parts require production date verification - turbo kits for pre-1991 models are incompatible with later units due to actuator linkage redesign (Mazda SIB 91-01).
The 20B-REW's primary reliability risk is thermal stress cracking in early rotor housings, with elevated incidence in sustained high-load driving conditions. Mazda Service Bulletin M-SB-91-03 documents increased housing failure rates linked to insufficient cooling flow and fuel octane sensitivity, while JAMA field reports note higher incidence in vehicles operated continuously above 5,000 rpm. Use of substandard fuel or prolonged high-RPM operation make lubrication integrity and coolant maintenance critical.
Analysis derived from Mazda technical bulletins (1989-1995) and Japan Automobile Manufacturers Association (JAMA) field data (1990-1996). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MAZDA 20B-REW.
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