McLaren M838T vs M840T Engines

Overview McLaren's road car lineup is powered by two generations of their in-house twin-turbocharged V8 engine: the M838T and its successor, the M840T . Both engines share a fundamental architecture — a flat-plane crank, twin-turbo V8 with a dry sump — but the M840T represents a significant engineering leap with 41% new components over the M838T. Understanding the differences between these two engines is essential for McLaren owners exploring ECU tuning, performance upgrades, and maintenance. Whether you're driving a 650S or a 720S, knowing your engine's strengths and limitations will help you make informed tuning decisions. McLaren M838T — The Foundation The M838T is a 3.8-liter twin-turbocharged V8 that served as the backbone of McLaren's road car range from 2011 to 2017. Co-developed with Ricardo Engineering, this engine established McLaren's reputation for lightweight, high-output powertrains. M838T Key Specifications Displacement: 3,799 cc (3.8L) Configuration: 90° V8, flat-plane crankshaft Induction: Twin turbochargers Block/Head Material: Aluminum alloy Valvetrain: DOHC, 32 valves, dry sump lubrication Bore x Stroke: 93mm x 69.9mm M838T Applications & Power Output Vehicle Power (HP) Torque (lb-ft) Years MP4-12C 592 443 2011–2014 650S 641 500 2014–2017 675LT 666 516 2015–2017 570S / 570GT 562 443 2015–2021 McLaren P1 (hybrid) 727 (903 combined) 531 2013–2015 The M838T was an impressive engine for its era, offering outstanding power-to-weight ratio. However, its turbocharger design and engine management calibration left significant headroom for tuning — making it a popular platform for ECU performance upgrades. McLaren M840T — The Evolution Debuting in the 2017 McLaren 720S, the M840T is a 4.0-liter twin-turbocharged V8 that builds on the M838T's architecture while introducing substantial improvements to power delivery, efficiency, and responsiveness. M840T Key Specifications Displacement: 3,994 cc (4.0L) Configuration: 90° V8, flat-plane crankshaft Induction: Twin-scroll turbochargers with titanium-aluminium turbine wheels Block/Head Material: Aluminum alloy Valvetrain: DOHC, 32 valves, dry sump lubrication Bore x Stroke: 93mm x 73.5mm (3.6mm longer stroke than M838T) New Components: 41% of parts are new vs. M838T M840T Applications & Power Output Vehicle Power (HP) Torque (lb-ft) Years 720S / 720S Spider 710 568 2017–2022 765LT / 765LT Spider 755 590 2020–2022 Artura (hybrid, V6 derivative) 577 (671 combined) 431 2022–present M838T vs M840T — Key Differences 1. Displacement & Stroke The most fundamental change is the increase from 3.8L to 4.0L, achieved entirely through a 3.6mm longer stroke (69.9mm → 73.5mm). The bore remains identical at 93mm. The longer stroke provides more torque at lower RPMs and improves overall engine efficiency. 2. Turbocharger Design The M840T uses new twin-scroll turbochargers with titanium-aluminium turbine wheels . These are lighter than the M838T's turbines, reducing rotational inertia for faster spool-up. Combined with electronically actuated wastegates , the M840T delivers sharper throttle response and reduced turbo lag compared to the M838T. 3. Cooling System The M840T features a completely redesigned cooling system with separate circuits for the engine block, cylinder heads, and turbochargers. This allows each component to operate at its optimal temperature, improving both power output and longevity under sustained high-performance use. 4. Internal Components With 41% new components, the M840T includes strengthened connecting rods, revised piston design for improved combustion efficiency, and upgraded bearings. The crankshaft is also revised to accommodate the longer stroke while maintaining the flat-plane firing order that gives McLaren engines their distinctive exhaust note. 5. Engine Management The M840T runs on an updated ECU platform with more sophisticated engine management software. This includes improved boost control algorithms, more precise fuel injection timing, and enhanced…