HEMI SWAP SHOP

 What Makes the Hemi Great?

5.7L Gen III Hemi Engine

As FCA (Fiat Chrysler Automobiles) recently celebrated “Hemi Day” on April 26, or 4/26, to honor the 426 cid Elephant Motor, we are reminded of the nearly 70 years of this iconic engine design that all started in 1950.

The original hemispherical combustion chamber engine design was introduced with the FirePower name for 1951 model-year Chrysler and was rated at 180 hp. The history of the Hemi is filled with plenty of memorable highlights such as Richard Petty’s dominance at the 1964 Daytona 500 where he lapped the field. Or “Big Daddy” Don Garlits breaking the 200-mph barrier with his 426 race Hemi.

With a rating of 345 horsepower, the Gen III 5.7L Hemi made its debut in 2003 in the Dodge Ram pickup. The third-generation engine is available in four cubic-inch displacements: 345, 370, 376, 392, but they’re more commonly referred to by their metric equivalent: 5.7L, 6.1L, 6.2L, 6.4L. The Gen III Hemi has even been on the “Ward’s 10 Best Engines” list six times from 2003 through 2007, and again in 2009.

The Hemi engine in the 2018 Dodge Challenger SRT Demon is derived from the “Hellcat” and produces 840 horsepower in stock trim from its supercharged 6.2L and runs on 100-octane race fuel. It produces 808 horsepower on 91-octane pump gas.

These are just a few of the highpoints of the Gen III Hemi, which ironically is not a completely hemispherical design anymore. With small “squish shelves” on both sides of the chamber, the center was hemispherical to incorporate big valves and ports that outflow LS1 heads by 24%. It also uses a coil-on-plug ignition system with not one, but two spark plugs per cylinder to shorten flame travel, leading to more consistent combustion and reduced emissions.

Chrysler added a Multi-Displacement System (MDS) in the original Hemi design to shut off two cylinders on each bank under light load to improve fuel economy. The main oil galleries supply oil directly to the solenoids that disable the lifters, and the oil for the lifters came down through the pushrods from the rockers up topside.

While the MDS system runs trouble-free in these engines, the first block wasn’t designed to include the variable valve timing (VVT) system. Chrysler had to redesign the Gen III block to incorporate its next evolution VVT in 2009. This redesigned Hemi can cruise in four-cylinder mode about 40 percent of the time, which is twice as much as the previous-generation MDS cylinder-deactivation system.

The rocker assemblies are about the only two things that carried over from the original Gen III design. While Chrysler made significant changes to the block and heads, there are some evolutionary upgrades also, including bigger valves and ports, updated cams and lifters along with a stronger crank and rods and a high-volume oil pump.

While there have been growing rumors of a replacement for the Hemi in the not too distant future as OEMs continue to downsize and add turbocharged direct injection systems, Chrysler has been selling around 400,000 trucks a year for a long time. That means there are a lot of Hemis in service that will need to be rebuilt sooner or later. When Chrysler updated the Hemi in 2009, it showed a pushrod engine could be modernized and perform well in many variations from cars to trucks. With the VVT upgrade making 400 lbs. ft. of torque, and the pickups with the active intake rated at 390 horsepower, these engines deliver decent fuel economy, and they’ve been virtually trouble-free. The trucks have held value and will be more likely to receive a new engine than cars.