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…
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 | Refer to vehicle handbook / manufacturer specification | |
Dry weight | 122 kg |
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.
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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.
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The 20B-REW can be reliable if maintained meticulously according to Mazda’s stringent service schedule. Early units (pre-1991) are susceptible to rotor housing cracking and turbo oil coking, but post-1991 revisions significantly improved durability. Consistent 5,000 km oil changes with Mazda Genuine Oil 10W-40, timely timing belt replacement, and exclusive use of RON 98 fuel are non-negotiable for longevity.
The most common issues are thermal stress cracking in early rotor housings due to cooling and fuel quality, turbocharger oil feed line coking from high heat, timing belt failure if not replaced at 40,000 km, and carbon buildup in side exhaust ports from poor driving habits or low-grade fuel.
The 20B-REW was fitted exclusively to the Eunos Cosmo (JC chassis) from 1989 to 1995, available in Type S and Type X trims. It was not used in any other production Mazda model, including the RX-7, which utilized the 13B-T and 13B-AP variants.
Limited tuning potential exists due to its original emissions-focused calibration and delicate rotor housings. While aftermarket turbo upgrades exist, they dramatically increase risk of housing cracking and apex seal failure. Stock outputs of 206 kW are already near the engine's safe mechanical limit; significant power gains compromise reliability without major internal reinforcement.
Real-world fuel economy is approximately 12–15 L/100km (19–23 mpg UK) under mixed driving. Its triple-rotor nature and twin-turbo system demand premium fuel (RON 98) and result in consumption typical of large-displacement V8 engines, despite its compact size.
Yes. The 20B-REW is an interference engine. If the timing belt fails, the rotors will collide with the intake and exhaust port edges, causing catastrophic damage to the housing, apex seals, and rotor tips. Immediate engine stoppage is required upon timing belt failure to minimize destruction.
Mazda specifies Mazda Genuine Oil 10W-40 (API SG) meeting JASO MA-1 for rotary engines. Synthetic blends are acceptable if certified to these specifications. Use of non-approved oils risks accelerated apex seal wear and turbo bearing failure. Change oil every 5,000 km regardless of driving conditions.
Comprehensive technical documentation and regulatory references
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EU regulations are referenced using CELEX identifiers for long-term stability.
EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
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