Multi-Displacement System
The Multi-Displacement System (MDS) is a variable displacement engine technology developed by Chrysler that seamlessly deactivates four cylinders in V8 engines during low-load cruising conditions to enhance fuel economy while maintaining full power output when needed.[1] Introduced in 2004 for the 2005 model year, MDS debuted on the 5.7-liter HEMI V8 in vehicles such as the Chrysler 300C and Dodge Magnum R/T, marking the first application of such technology in sedans and later expanding to SUVs like the 2005 Jeep Grand Cherokee and pickups including the 2006 Dodge Ram 1500.[1][2] MDS operates by using electronic controls and specialized solenoids to redirect engine oil pressure, which collapses the valve lifters on cylinders 1, 4, 6, and 7, preventing their intake and exhaust valves from opening and effectively shutting off fuel injection to those cylinders.[3] This transition between four-cylinder and eight-cylinder modes occurs in as little as 40 milliseconds, allowing the remaining active cylinders to handle the load with minimal perceptible change in vehicle performance or sound, thanks to integrated exhaust tuning that preserves the signature V8 rumble.[1][2] The system is controlled by the engine's powertrain control module, which monitors throttle position, vehicle speed, and load to activate deactivation seamlessly during steady-state driving.[3] Key benefits of MDS include up to a 20% improvement in fuel economy under light-load conditions, contributing to an estimated annual savings of 60 million gallons of fuel across equipped vehicles by 2007.[1][3] It has been applied in various Chrysler, Dodge, Jeep, and Ram models featuring 5.7-liter and 6.4-liter HEMI engines, such as the Dodge Charger R/T, Durango, and Jeep Commander, and is also used in some heavy-duty applications, such as the Ram 2500 and 3500 with the 6.4 L HEMI engine.[1][2] While praised for balancing efficiency and performance, the system has faced criticism for contributing to camshaft and lifter failures, leading many owners to disable it, and introduces additional components like deactivation solenoids and modified lifters, which can be prone to wear over time.[3][4]Overview
Definition and Purpose
The Multi-Displacement System (MDS) is Chrysler's proprietary variable displacement technology for V8 engines, enabling seamless deactivation of four cylinders during light-load conditions to operate effectively as a four-cylinder engine, thereby optimizing fuel consumption.[1] This system integrates directly into the engine's design, allowing it to alternate between full eight-cylinder operation for peak performance and reduced-cylinder mode for efficiency without altering the engine's core architecture.[1] The primary purpose of MDS is to deliver a balance of robust V8 power and enhanced fuel economy, particularly in scenarios requiring minimal acceleration, while minimizing emissions and preserving vehicle drivability.[1] By deactivating cylinders under steady-state conditions like highway cruising, it reduces pumping losses and fuel delivery to unused cylinders, targeting up to 20% improvement in fuel economy during such operations.[1] This approach ensures drivers experience no perceptible change in performance or smoothness during mode transitions.[1] Variable displacement concepts originated in the 1980s with early implementations like General Motors' Cadillac V8-6-4 engine, which aimed to address fuel efficiency amid oil crises but faced reliability issues due to nascent electronic controls.[5] MDS represents a modern refinement of this idea, tailored for overhead-valve (OHV) pushrod engines such as the HEMI V8, leveraging advanced engine management for reliable operation.[6]History and Introduction
The Multi-Displacement System (MDS), a cylinder deactivation technology designed to enhance fuel efficiency by allowing V8 engines to operate on four cylinders during light-load conditions, was developed by Chrysler's powertrain engineering team in the early 2000s. This innovation emerged amid escalating Corporate Average Fuel Economy (CAFE) standards, which required automakers to improve fleet-wide efficiency, and surging global oil prices that began climbing significantly from 2003 onward, pressuring the industry to balance performance with economy.[7][8] MDS debuted in the 2005 model year on the 5.7 L HEMI V8 engine, marking its first high-volume production application in North American vehicles with the Chrysler 300C and Dodge Magnum R/T.[9] The system was extended to pickup trucks the following year in the 2006 Dodge Ram 1500, making Chrysler the first to offer cylinder deactivation in that segment.[10] These initial implementations focused on integrating MDS seamlessly into the HEMI architecture to support fuel savings without compromising the engine's power delivery. Key milestones in MDS evolution included its expansion to larger-displacement HEMI variants, such as the 6.4 L engine introduced in 2011 for high-performance applications.[11] In 2009, Chrysler integrated Variable Cam Timing (VCT)—also known as Variable Valve Timing (VVT)—with MDS on updated 5.7 L HEMI engines, enabling smoother mode transitions and broader operational efficiency.[12] Starting around 2019, MDS was paired with the eTorque mild-hybrid system in select models for further efficiency gains. Following the 2021 formation of Stellantis, MDS continued in production HEMI engines, including the 6.4 L variant for heavy-duty applications as of 2025, with a focus on durability enhancements. The 5.7 L HEMI V8 with MDS and eTorque returned to the Ram 1500 lineup for the 2026 model year after its discontinuation in the 2025 model.[13][14]Technical Operation
Cylinder Deactivation Mechanism
The Multi-Displacement System (MDS) in Chrysler's HEMI engines employs specialized hydraulic roller lifters equipped with internal locking pins to achieve cylinder deactivation. These lifters are installed on cylinders 1, 4, 6, and 7, allowing the engine to operate in a four-cylinder mode during low-load conditions. When deactivation is initiated, multi-displacement solenoids—two per cylinder bank—direct pressurized engine oil into the lifters, forcing the locking pins to retract and collapse the lifter assembly. This collapse decouples the pushrods from the camshaft, preventing the intake and exhaust valves from opening on the targeted cylinders.[15][16][3] Simultaneously, the electronic control module (ECM) disables fuel delivery to the injectors and cuts spark to the ignition coils of the deactivated cylinders, ensuring no combustion occurs and avoiding potential misfires. In this state, the pistons in the deactivated cylinders continue to reciprocate, driven by the crankshaft linkage to the active cylinders, effectively serving as a "prime mover" to maintain smooth rotation without active compression or expansion cycles in those chambers.[15][16] The system relies on the engine's oil pressure, typically maintained between 40 and 60 psi, which is routed through the solenoids to either hold the lifter plungers extended (in eight-cylinder mode) or release them for collapse (in four-cylinder mode). Each solenoid operates at a resistance of approximately 10.3 ohms and responds to ECM signals to modulate this pressure precisely.[15][16][17] Transitions between modes occur seamlessly in less than 40 milliseconds, enabled by the rapid solenoid response and oil flow dynamics, resulting in imperceptible shifts to the driver. This quick actuation is facilitated by the pushrod valvetrain design of the HEMI engine, which positions the camshaft in the block and allows simpler lifter-based deactivation compared to overhead cam configurations that would require more complex rocker arm switching mechanisms.[15][16][18]Control and Activation
The Powertrain Control Module (PCM), serving as the central electronic control unit, oversees the Multi-Displacement System (MDS) by continuously monitoring key engine and vehicle parameters through an array of sensors to decide on cylinder activation or deactivation. These sensors include the throttle position sensor for detecting pedal input, the manifold absolute pressure (MAP) sensor for assessing engine load, the vehicle speed sensor for tracking road conditions, and the engine coolant temperature sensor for ensuring optimal operating temperatures. When suitable conditions are met, the PCM issues commands to engage MDS, seamlessly transitioning the engine from eight-cylinder to four-cylinder operation while maintaining smooth performance.[15][16] MDS activation occurs under specific steady-state conditions designed to maximize fuel efficiency without compromising drivability, typically when engine speed is between approximately 1,000 and 3,000 RPM, throttle input remains steady at under 20% or light load, vehicle speeds are above approximately 20 mph in steady highway cruising up to around 80 mph, and acceleration is light or absent. The system disengages rapidly—within 0.04 seconds—upon detection of increased throttle demand, braking, or any abrupt change in load, reverting to full-cylinder operation to deliver immediate power. This logic prioritizes scenarios like highway cruising where power needs are minimal, ensuring the deactivated cylinders (1, 4, 6, and 7) do not contribute to combustion during these periods.[15][18][19][20] Four multi-displacement solenoids—two per cylinder bank—facilitate the mechanical execution of deactivation by pulsing at 12 volts under PCM command to redirect pressurized engine oil flow, locking or unlocking the valve lifters as needed. In the event of a solenoid fault, such as electrical malfunction or oil flow restriction, the system defaults to full eight-cylinder mode to prevent potential engine damage, with the PCM logging the error for diagnostics.[16][21] To ensure imperceptible transitions, MDS integrates closely with the electronic throttle control (ETC) system, which adjusts air intake, and torque management algorithms that fine-tune ignition timing and fuel delivery to mask any mode shifts. In models produced after 2009, the system further incorporates variable valve timing (VVT) to optimize camshaft phasing during activation and deactivation, enhancing smoothness and efficiency.[15][18] Diagnostic capabilities are embedded within the On-Board Diagnostics II (OBD-II) framework, with specific trouble codes such as P3401, P3424, P3441, and P3449 indicating solenoid circuit faults on cylinders 1, 4, 6, and 7 respectively. The PCM performs self-test routines during engine startup, cycling the solenoids to verify operation, and technicians can use scan tools to command activation for further testing, including resistance checks (typically 10.3 Ω ± 0.25 at 68°F).[16][22]Applications
Compatible Engines
The Multi-Displacement System (MDS) is integrated into select variants of Chrysler's Gen III HEMI V8 engines, enabling cylinder deactivation for improved fuel efficiency under light loads. The primary engine featuring MDS is the 5.7 L (345 cu in) HEMI V8, introduced in 2003 and produced to the present, with MDS becoming standard on most automatic transmission-equipped models starting in 2006. This engine delivers power outputs ranging from 345 to 395 horsepower, depending on the application and tuning, while incorporating MDS-specific components such as specialized hydraulic roller lifters and deactivation solenoids in the valvetrain to manage cylinder shutoff without compromising structural integrity. Its bore and stroke measure 99.5 mm x 90.9 mm, supporting a compression ratio typically around 9.6:1 in MDS-equipped versions.[12][23][24][25] Another key compatible engine is the 6.4 L (392 cu in) HEMI V8, in production since 2011 and continuing into the present under Stellantis. MDS is standard on automatic transmission variants, particularly in truck and performance applications, where it deactivates four cylinders during low-demand conditions. Power output varies by model, reaching 410 horsepower in heavy-duty truck configurations and up to 485 horsepower in SRT performance variants. The engine's bore and stroke are 103.9 mm x 94.6 mm, with a forged steel crankshaft and reinforced valvetrain elements designed to accommodate MDS operation alongside higher-output demands.[26][11][27][11] Certain variants and applications exclude MDS for performance or market-specific reasons. The 5.7 L HEMI Eagle economy tune, a detuned version optimized for lower emissions and fuel economy in select markets, omits MDS to simplify the valvetrain and reduce costs, relying instead on variable valve timing alone. Similarly, some export models, particularly those paired with manual transmissions or tuned for non-U.S. regulations, lack MDS. High-performance supercharged engines like the 6.2 L Hellcat HEMI (2015-2023) do not incorporate MDS, prioritizing consistent power delivery over deactivation efficiency.[28][18][18] As of 2025, MDS remains retained in non-hybrid V8 configurations under Stellantis, including updated 5.7 L and 6.4 L variants adapted for Euro 7 emissions standards through refined fuel management and catalytic converter integration in markets such as Europe, where the 2026 Ram 1500 will offer the 5.7 L HEMI eTorque with MDS. MDS is also included in eTorque mild-hybrid V8 applications for load balancing alongside electric assist.[24][13][29]| Engine Variant | Displacement | Bore x Stroke (mm) | Power Output (hp) | MDS Availability | Production Years |
|---|---|---|---|---|---|
| 5.7 L HEMI V8 | 5.7 L (345 cu in) | 99.5 x 90.9 | 345-395 | Standard on most auto variants; excluded in Eagle tune and some exports | 2005-present |
| 6.4 L HEMI V8 | 6.4 L (392 cu in) | 103.9 x 94.6 | 410 (trucks) to 485 (SRT) | Standard on auto variants | 2011-present |
| 6.2 L Hellcat Supercharged | 6.2 L (376 cu in) | 103.9 x 86.0 | 707+ (supercharged) | Not available | 2015-2023 |