Counter Talk: Chrysler Multi-Displacement System

For those who are old enough to remember the Cadillac V8-6-4 engine of the early 1980s, the topic of variable displacement can send shivers up the spine.

That power plant was fraught with problems–getting stuck in one mode or another led many owners to demand the system be disconnected, and even today die-hard Cadillac fans see it as a black mark on an otherwise fine marque.

Over at DaimlerChrysler, the engine development department has no such progenitor to overcome, in the lab or the marketplace, in creating the Multi-Displacement System standard on the 5.7 litre Hemi engine beginning in the 2005 model year. Found on the 300C, Magnum RT, and Grand Cherokee, the engine uses a system of integrated controls to transition from eight cylinders to four in just 40 milliseconds.

Some of the significant technologies enabling the Chrysler Group MDS are the speed of electronic controls, the sophistication of the algorithms controlling the systems, and the use of Electronic Throttle Control.

The MDS system employs oil pressure to engage and disengage valve lifters, keeping those four cylinders completely closed off. In addition to the fact that there is no combustion, energy is not lost by pumping air through these cylinders.

The basic goal is fuel savings, and the company says that customers will experience estimated fuel economy gains of up to 20% under various driving conditions, and a projected 10% aggregate improvement. Improved fuel economy is realized without any change in customer experience–drivers will receive the benefit without changing their driving habits and without compromising style, comfort, or convenience.

For those aching for facts and figures, the 5.7-litre Hemi engine is an internally balanced pushrod, OHV 90-degree V-8. The cast iron block is a deep-skirt design with cross-bolted main bearing caps. The aluminum cylinder heads feature two valves per cylinder, hemispherical combustion chambers with dual spark plugs, and coil-over-plug ignition. An Integrated Air-Fuel Module (IAFM) incorporates the function of 26 individual components in the induction and fuel system, thereby reducing cost, weight, and engine plant complexity.

It also marks the Chrysler Group’s first application of an electronic throttle control in a rear-wheel-drive vehicle.

So far, more than two years into production, there have been no problems reported with the engine, with the possible exception of one engine with a valve-timing anomaly. According to valve train parts manufacturers, the AERA-Engine Rebuilders Association, and DaimlerChrysler itself, so far, so good. In fact, Chrysler says that there should not be any challenges for rebuilders specific to MDS other than an additional wiring harness and four solenoids installed in the lifter valley.

Specifications

*Type and description: Eight cylinders, 90-degree V-type, liquid cooled

*Displacement: 345 cu. in. (5.7-litre)

*Bore x stroke: 3.92 in. x 3.58 in. (99.5 mm x 90.9 mm)

*Valve system: Pushrod- operated overhead valves, 16 valves (eight deactivating, eight conventional when equipped with Multi-Displacement System), hydraulic roller lifters

*Fuel injection: Sequential, multi-port, electronic, returnless

*Construction: Deep-skirt cast iron block with cross-bolted main bearing caps. Aluminum alloy heads with hemispherical combustion chambers

*Compression ratio: 9.6:1

*Power (SAE net): 345 hp (257 kW) @ 5400 rpm, (61.0 hp/L), truck applications; 340 hp (254 kW) @ 5000, passenger vehicle applications

*Torque (SAE net): 375 lb.-ft. (508 Nm) @ 4200 rpm, truck applications; 390 lb.-ft. (525 Nm) @ 4000, passenger vehicle applications

*Max. engine speed: 5800 rpm (electronically limited)

*Fuel requirement: Unleaded mid-grade, 89 octane (R+M)/2 – recommended; Unleaded regular, 87 octane (R+M)/2 – acceptable

*Oil capacity: 7 qt. (6.6L)