Chrysler Hemi from 2003—The Third Generation—part 5 of 5

Chrysler’s third-generation Hemi introduced a two-spark-plug-per-cylinder ignition system and eventually spawned everything from a fuel-saving 5.7-liter truck engine to a 590-horsepower 426-cubic-inch showstopper. Along the way, displacements ranged from 5.7 to 6.4 liters, with technologies like MDS cylinder deactivation and variable crankshaft timing added throughout its run. Read on to find out how one ignition change led to an entire engine family.

Two spark plugs per cylinder sounds like the kind of spec sheet detail nobody outside an engineering department would ever care about. But that single change, tucked into the third generation of Chrysler’s modern Hemi, quietly reshaped how the engine breathed, how clean it ran, and eventually how many different displacements Chrysler would build around the same basic architecture. By the time this engine family was finished evolving, it had spawned everything from a fuel-sipping truck motor to a 590-horsepower concept car showstopper. How did one ignition change lead to all of that?

A New Way to Light the Fire

The generation three Hemi departed from its predecessors in a fundamental way: it adopted a coil-on-plug, distributorless ignition system using two spark plugs per cylinder instead of one. That setup shortens the distance the flame front has to travel across the combustion chamber, which improves combustion completeness and reduces emissions as a direct result. The cylinders themselves also moved away from a totally hemispherical shape, the design feature the Hemi name originally referenced, in favor of a chamber geometry better suited to modern emissions requirements. Despite that shift, the 5.7-liter version still managed to hold onto the historically significant one-horsepower-per-cubic-inch rating, though it’s worth noting the rating method changed too, from the older Gen 2 SAE gross horsepower standard to the more conservative and accurate SAE net system.

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MDS: An Engine That Can Run on Half Its Cylinders

One of the more clever pieces of engineering in the Gen 3 Hemi is the Multi-Displacement System, or MDS, which shuts down two cylinders entirely under light load conditions to reduce fuel consumption. Combined with variable valve timing, this technology delivered roughly a 4 percent improvement in fuel mileage on applicable models, a meaningful gain for an engine family built around large-displacement V8s. MDS wasn’t available across the board, though; Chrysler left it out of the Durango and Aspen SUVs, the upscale sedan trims, and every high-performance Charger and Challenger paired with a six-speed manual transmission, since those applications prioritized consistent power delivery over incremental fuel savings.

The 5.7 Goes to Work in Trucks and Sedans

A 5.9-liter Hemi replaced the outgoing Magnum 5.9-liter engine across the Dodge Ram 1500, 2500, and 3500 lineup starting in 2003, but it was the 345-cubic-inch 5.7-liter version that became the workhorse of the family. In Ram applications, that 5.7 delivered 345 horsepower and 375 pound-feet of torque, while the same basic engine tuned for the Chrysler 300C and Magnum R/T made a slightly lower 340 horsepower but was still credited with roughly 100 more horsepower than the 5.9-liter engine it replaced in sedan applications. Built as a 90-degree V8 with two valves per cylinder, a 3.917-inch bore, and a 3.578-inch stroke, this engine earned a spot on Ward’s list of the ten best engines for the 2003 through 2007 model years, then again in 2009.

Variable Valve Timing Arrives

The most significant change to the 5.7 Hemi between the 2008 and 2010 model years was the introduction of variable valve timing, which Chrysler branded as VCT, for variable crankshaft timing. The system controls oil flow through an unusual phasing mechanism on the camshaft sprocket, allowing the engine to advance or retard cam timing on demand. Starting in 2009, the 5.7 offered five distinct camshaft configurations built around VCT, paired with a revised cylinder head shape for improved flow and model-specific intake manifolds. Some applications, excluding the Durango and Aspen, used an active intake manifold with a short runner valve that closes at low rpm to concentrate airflow, then opens as acceleration increases to maximize both horsepower and torque higher in the rev range.

Bigger Displacements Join the Family

Chrysler didn’t stop at 5.7 liters. A 6.1-liter version, displacing 369.7 cubic inches with a 4.06-inch bore, produced 425 horsepower and 420 pound-feet of torque at 4,800 rpm, built with different cooling channels than the smaller 5.7 and using oil jets specifically for piston cooling and lubrication under higher loads. That engine also received a forged crankshaft, heavy-duty connecting rods, and lighter pistons for a genuinely stronger bottom end. A related 6.1-liter variant used an aluminum cast intake tuned specifically for high-rpm operation and skipped both the Multi-Displacement System and variable valve timing entirely, prioritizing consistent high-output performance over the fuel-saving technology found elsewhere in the family.

The 392 and the Rise of the Apache

A 6.4-liter, 392-cubic-inch Hemi first appeared as a crate engine option in 2007 and made its way into a production car for the first time with the 2011 SRT8 lineup, producing up to 525 horsepower and 510 pound-feet of torque using aluminum alloy pistons in a design closely related to the 6.1. That engine found its way into the 2011 SRT8 lineup before Chrysler revised the block design further, nicknaming the newest version the ‘Apache,’ based on the third-generation 5.7 Hemi architecture despite sharing surprisingly few components with the earlier crate 392. The revised Apache-based 392 produced 470 horsepower and 470 pound-feet of torque, and found homes in the SRT8, the 300C, the Grand Cherokee, and special edition Chargers wearing the badging to prove it.

A Preview of Where the Hemi Was Headed

In 2012, Chrysler used the Detroit auto show to show off just how far this engine family could be pushed, debuting a 426-cubic-inch Hemi V8 rated at 590 horsepower under the hood of the Dodge Charger Redline concept car. That figure, nearly double what the original 5.7-liter Gen 3 Hemi produced at launch, demonstrated exactly how much headroom Chrysler had engineered into this architecture from the start. From a two-spark-plug ignition system built for cleaner emissions to a 590-horsepower show car engine, the third-generation Hemi’s evolution shows how much performance ceiling can hide inside what looks, on paper, like an emissions-driven redesign.

A Reputation Built on Reliability as Much as Power

Beyond the horsepower figures and displacement variations, the Gen 3 Hemi built its reputation on genuine long-term reliability, a trait not every high-output V8 from this era can claim. The combination of a forged crankshaft in the larger displacement versions, robust bottom-end architecture inherited across the family, and Chrysler’s willingness to keep refining components like the Multi-Displacement System through multiple revisions meant these engines routinely accumulated well over 150,000 miles in daily service without major issues, even in performance-oriented trims. That durability record is a big part of why the Gen 3 Hemi remained in production across so many Chrysler, Dodge, and Jeep platforms for as long as it did, from work trucks all the way up to the SRT8 halo cars.

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