Mazda 20B Engine for Sale | OEM Used Legendary 20B-REW Triple-Rotor Sequential

Description

About the Mazda 20B-REW Triple-Rotor Sequential Twin-Turbo Rotary Engine

Looking for the legendary Mazda 20B triple-rotor rotary engine? Part Nests stocks OEM used Mazda 20B-REW sequential twin-turbo rotary engines from Eunos Cosmo / JC Cosmo (1990-1995) donor vehicles. The 20B-REW is the only triple-rotor production engine Mazda ever produced, representing the absolute pinnacle of Mazda rotary engineering. With 2.0 liters of effective displacement across THREE rotors (vs the conventional twin-rotor 13B), sequential twin-turbocharging via the Hitachi HT-12 and HT-15 system, and 280 PS (276 HP) factory rating in the JDM market (likely closer to 300 plus HP in reality due to the JDM gentlemen’s agreement horsepower cap), the 20B-REW represents the high-water mark of rotary performance from any production rotary engine ever built. Whether you are building a legendary 20B swap into an FD RX-7 chassis, restoring a JC Cosmo grey-market import, or sourcing for a serious rotary performance project, this listing covers the OEM Mazda 20B-REW from JC Cosmo donor vehicles.

Engine Overview: The 20B-REW Triple-Rotor Architecture

The Mazda 20B is fundamentally different from any other production engine. Understanding the architecture is critical:

• Configuration: Triple-rotor Wankel rotary engine (NOT a piston engine; uses THREE spinning triangular rotors instead of two like the more common 13B family)
• Effective Displacement: 2.0 liters (three 654 cc rotor chambers, total 1,962 cc effective)
• Sequential twin-turbocharged via Hitachi HT-12 (smaller primary, spools first) and HT-15 (larger secondary, kicks in at higher RPM) turbochargers in sequential arrangement
• Peripheral exhaust ports (the older rotary architecture, not the Multi-Side Port Renesis evolution)
• 280 PS factory rating (the JDM “gentlemen’s agreement” 276 HP horsepower cap; likely 300 plus HP in reality)
• 295 lb-ft peak torque at relatively low RPM (sequential turbo system spools quickly with the smaller primary)
• Longer 3-rotor eccentric shaft (with intermediate stiffening between rotors)
• Three sets of apex seals, side seals, and corner seals (vs two on conventional 13B)
• Six spark plugs total (two per rotor, leading and trailing)
• JDM-only production (never sold new in US market; all US-located 20B engines are gray-market imports or rebuilds)

Eunos Cosmo / JC Cosmo Donor Application

The 20B-REW was used in only ONE production vehicle: the Eunos Cosmo (also known as the JC Cosmo). Context:

• Vehicle: Eunos Cosmo (JC Cosmo platform) 1990-1995, JDM-only flagship coupe sold through Mazda’s Eunos premium brand network in Japan
• Production: Limited production approximately 8,800 units total over the 1990-1995 production run
• Market positioning: Flagship grand-tourer luxury coupe, priced as Mazda’s premium model in the Japanese domestic market
• Engine options: Eunos Cosmo offered 13B-REW (twin-rotor, twin-turbo) and 20B-REW (triple-rotor, twin-turbo) options; the 20B-REW was the premium engine option representing approximately half of production
• US market: NEVER sold new in US market; all US-located 20B engines are gray-market imports (the 1990-1995 vehicles became legally importable to US under the 25-year rule starting 2015-2020 depending on production year)

The Sequential Twin-Turbo System

The 20B-REW uses Mazda’s sequential twin-turbo system, shared with the FD RX-7 13B-REW but adapted for the three-rotor displacement:

• HT-12 primary turbo: Smaller turbocharger, spools at lower RPM to provide low-end torque and immediate throttle response
• HT-15 secondary turbo: Larger turbocharger, kicks in at higher RPM to provide top-end power; sequential arrangement means the secondary turbo joins the primary above approximately 4,500 RPM
• Sequential arrangement: Primary turbo operates alone at low RPM (eliminating turbo lag of a single large turbo), then sequential transition activates the secondary turbo for top-end power
• Twin-Scroll plumbing: Complex pipe routing between the two turbos with multiple wastegates and bypass valves
• Common failure point: The sequential changeover plumbing is complex and develops vacuum leaks / actuator failures over time, requiring careful inspection during engine purchase

20B vs 13B: Why the Triple-Rotor Matters

The triple-rotor 20B-REW vs the twin-rotor 13B-REW (per our / listings) is a fundamental architectural difference:

• Displacement: 20B has 2.0L effective (50% larger than 13B’s 1.3L); proportionally more power and torque
• Smoothness: Triple-rotor engines run smoother than twin-rotor engines, similar to how V8s run smoother than V4s in piston engines
• Power potential: 20B can produce 400-500 plus HP in modified form, well above 13B-REW’s 350-450 HP capability
• Complexity: Triple-rotor is more complex (more rotors, more apex seals, longer eccentric shaft, longer engine length)
• Rarity: 20B production was limited to JC Cosmo; 13B production spanned RX-7 generations and JDM Capella / Luce / Cosmo applications
• Cost: 20B engines command substantial premium over 13B-REW engines due to rarity and triple-rotor uniqueness

Mazda Rotary Engine Family Context

The Mazda 20B-REW triple-rotor (this listing) is the absolute pinnacle of Mazda rotary engineering, representing the high-water mark of rotary performance. For complete Mazda rotary engine family context across our catalog: the Mazda RX-8 13B-MSP Renesis (our listing, the modern naturally-aspirated Multi-Side Port rotary engine for the RX-8 2004-2012 application, the final mass-production Wankel rotary engine before Mazda ended rotary production after the RX-8 in 2012) is the modern naturally-aspirated rotary representing rotary at its emissions-compliant conclusion. The Mazda RX-7 13B engine (our listing, the legendary 13B Wankel rotary across multiple RX-7 generations including 12A naturally-aspirated, 13B naturally-aspirated, 13B-T turbocharged, 13B-REW twin-turbo for the FD RX-7) is the predecessor 13B family across the RX-7 generations including the turbocharged variants. The Mazda 13B engine family overview (our listing, the comprehensive 13B family overview covering the broader 13B Wankel rotary engine family) is the family-overview listing unifying the 13B family from FB / FC / FD RX-7 through RX-8. Four Mazda rotary engine listings across : 13B-MSP Renesis modern NA for RX-8, (this listing) 20B-REW triple-rotor twin-turbo for Cosmo (the pinnacle), 13B Wankel for RX-7 across generations, 13B family overview. For piston-engine Mazda context, the Mazda CX-9 SkyActiv-G 2.5T, Mazda CX-7 L3-VDT MZR DISI, and Mazda MX-5 cover the Mazda piston-engine lineup; plus the Mazda 3 water pump is the related Mazda piston-engine cooling system component.

Critical Buyer Information: 20B Engine Realities

The 20B-REW is a specialty engine with substantial buyer considerations:

• JDM-only history: No US-market production, no US-market dealer support, no US-market parts catalog. All servicing requires specialty rotary shops experienced with JDM imports.
• Rarity premium: 20B engines command 3-5x the price of 13B-REW engines due to limited production (8,800 Cosmos vs 30,000 plus FD RX-7s) and triple-rotor exclusivity.
• Sequential twin-turbo complexity: The HT-12 / HT-15 sequential system requires specialist diagnosis; vacuum leaks and actuator failures are common in aging units.
• Apex seal wear (3 rotors): Triple the apex seal wear surfaces vs twin-rotor; rebuild costs proportionally higher.
• Oil consumption (3 rotors): Triple-rotor consumes more oil than twin-rotor (proportional to rotor count); expect 1 quart per 800-2,000 miles.
• Parts availability: Some 20B-specific parts (eccentric shaft, sequential turbo components, intake / exhaust manifolds) are limited; Atkins Rotary and other specialty shops carry inventory.
• Engine swap complexity: 20B is longer than 13B (three rotors vs two), requires transmission adapters for non-Cosmo applications, requires custom intake / exhaust / fuel system for swaps.

Vehicle Compatibility

20B-REW Architecture Specifications

Sequential Twin-Turbo System Documentation

Maintenance and Service Requirements

Engine Swap and Application Reference

Why Buy From Part Nests

• Engine variant verified as 20B-REW triple-rotor (NOT the more common twin-rotor 13B-REW /)
• Donor confirmed (Eunos Cosmo / JC Cosmo 1990-1995 JDM-only flagship coupe)
• Compression tested all THREE rotor housings (each face of each rotor measured)
• Sequential twin-turbo system condition assessed (HT-12 primary / HT-15 secondary Hitachi twin-turbo arrangement)
• Apex seal condition documented all three rotors
• Eccentric shaft condition verified (longer 3-rotor eccentric shaft with intermediate stiffening)
• Rotor housing wear documented (peripheral exhaust ports older rotary architecture)
• Honest disclosure of rotary engine maintenance requirements and JDM-import specifics
• Specialty freight handling for rare rotary engines
• 15 day replacement warranty on internal defects (limited per rotary engine standards)
• JDM rotary specialist support team familiar with 20B specific requirements
• Call (855) 634-4447 for fitment confirmation and to lock in your order.