Chrysler Hemi Continues to Evolve

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Story Behind 10 Best Engines

A guy is towing a 1960s-era Dodge Charger behind a new Dodge Ram Heavy Duty pickup. Two scruffy characters in an old Plymouth Barracuda pull up beside him at a light. “Hey,” queries one, “That thing got a Hemi?”

“Yeah!” The pickup driver responds. “Sweet!” says Scruffy One, nodding knowingly at Scruffy Two.

When the light changes, the Barracuda takes off, but the truck with trailer beats it to the next light. Barracuda guys are stunned. “Did you mean the Charger?” Pickup Guy asks, gesturing back at his trailer to slack-jawed nods from the ‘Cuda. “Cause, you know, that’s got a Hemi, too.”

Most recall that ad for Chrysler’s then-new 5.7L “Hemi” V-8, which first debuted in the ’03 Dodge heavy-duty pickups.

That engine won Ward’s 10 Best Engines honors five years in a row, and the latest version recently made the 2009 list.

Related to past legendary Hemis mostly in combustion chamber philosophy, the new one debuted with 345 hp and 375 lb.-ft. (508 Nm) of torque, 41% more power and 12% higher torque than the 5.9L V-8 it replaced.

“One enabler for increasing output is getting the engine to breathe very, very well,” Bob Lee, then Chrysler Group director of rear-wheel-drive engine engineering, said at the time. “We wanted airflow and knew how to get it – hemi head, big valves – and how to use analytical techniques to control it. Then we used dual spark plugs to get the burn rate we needed.”

Hemi tested in ’09 Dodge Challenger R/T and Ram fullsize pickup.

A hemisphere is half of a sphere, so we asked what made this engine a “hemi.”

Two things, Lee said. “One is the shape of the combustion chamber. The old 426 Hemi’s chamber wasn’t technically a hemi; it was a section, not half of a sphere. This one is similar but a smaller section.”

The other feature that makes it similar to the original Hemi is the placement of the valves, opposite each other with their centerlines perpendicular to the crankshaft, Lee says.

When work began on the redesigned engine in 1997, “We realized we had an opportunity to span the full range, from a work truck to a luxury passenger car. But because the wants and needs of car and truck customers are very different, one major challenge was blending both to accommodate that stretch,” says Lee, now vice president-Powertrain Product Team at Chrysler LLC.

The new Hemi V-8 soon expanded into light-duty pickups, SUVs and Jeeps; Chrysler 300C, Dodge Magnum and Charger cars; and high-performance SRT models. “All these things were planned from day one,” Lee says, “including the things we just put in for the ’09 model year. And we planned from the beginning for the fuel economy to be substantially improved with some later mechanism, which ultimately led to cylinder deactivation.

“So the team designed the necessary oil passages into the block and heads for what became the Multi-Displacement System (MDS).”

Did Chrysler know at the time that General Motors Corp. engineers were working on a similar cylinder deactivation strategy?

“Any good engine engineer looks at losses in an engine,” Lee says. “Pumping losses are one of the most significant areas and one of the most difficult trade-offs when you do a work product and a passenger-car product off the same base, because the work product needs immense displacement and torque capability and a fair amount of power. If you use a similar engine in a passenger car, you end up running throttled a huge amount of the time.”

There are a number of ways of going after those losses. “We looked at variable valve timing,” Lee continues, “and the first Hemi designs we laid out were overhead-cam versions.

“But we couldn’t fit them into the packaging space, so we ended up with a cam-in-block design. Once you make that decision, cylinder deactivation is almost a no-brainer. GM was working with Eaton (Corp.) here in the U.S., we were working with INA in Germany (part of the Schaeffler Group), and we didn’t realize until late in the program there were competitive systems. But we got it to production first.”

Chrysler’s system shuts down every other cylinder at light loads by decoupling inner and outer bodies of specially designed lifters for their intake and exhaust valves. The inner bodies have a pair of pins that extend in response to oil pressure to lock them to the outer bodies. When that oil pressure is relieved, the pins retract so the inner bodies can move inside the outer bodies, decoupling those valves from the camshaft and keeping them closed.

“The process is a lot more complicated than it looks,” Lee says. “You’ve got a few milliseconds during transitions to dynamically match the torque of a 4-cyl. engine to that of an 8-cyl. engine, and you don’t want to transmit 4-cyl. torsional characteristics into the vehicle. And when you’re running on four cylinders, skipping every other cylinder of a V-8, you get a strange sputtering exhaust sound.”

The team worked very hard to tune that out, which took a lot of simulation and testing. This engine’s exhaust note at any rpm proves the effort was successful.

Most importantly, the all-new ’09 Hemi can cruise in fuel-saving 4-cyl. mode up to 70 mph (112 km/h) and as much as 40% of the time, both major improvements over the ’08 engine. This enabled a number of Ward’s judges to top 19 mpg (12.3 L/100 km) with the Hemi, putting it in line with certain premium V-6s tested.

In what other ways does this new iteration differ from its’03-’08 predecessors? Dean Tomazic, a vice president of FEV, an independent engineering company that worked with Chrysler on the engine, points out three significant advancements: First, a higher compression ratio of 10.5:1 vs. the previous 9.6:1 improves the combustion process, and therefore efficiency.

Second, a new cam-phasing system provides variable valve timing (VVT) for improved breathing and volumetric efficiency. Third, an “active air intake manifold” on the pickup and SUV version offers variable runner lengths to expand the engine’s torque and power ranges. “It has short runners for high speeds,” Tomazic explains, “and longer runners for lower speeds.”

The trick is butterfly valves in the circular runners that open to a 50% shorter intake path during hard acceleration above 4,000 rpm, one good reason the ’09 truck version is rated at 390 hp and 407 lb. ft. (552 Nm) vs. the Challenger R/T’s slightly tamer 376 hp and 410 lb. ft. (556 Nm) with a 6-speed manual transmission.

Evolutionary upgrades include larger valves; higher camshaft lifts; freer-flowing ports, intake and exhaust systems; crankshaft structural upgrades; a dual-mass crankshaft damper; new valve spring; floating-pin piston designs and an oil-pump capacity increase.

But why would Chrysler (like GM) carry on with pushrod V-8s when the rest of the world has long gone to smaller overhead-cam designs? “You write down the requirements and look for solutions to meet them,” Lee responds. “Spinning (the engine) to 7,000 rpm was not a requirement.”

In addition to the lower cost, smaller package size and ease of implementing MDS, Lee adds Chrysler engineers would have needed a “substantial invention” to get the pumping losses out of an OHC engine.

“When we looked at those things, we could take a lot of money out of the OHC and use it to pay for the MDS and still meet all the power and torque requirements.”

This improved version of the Hemi “is a fairly low-cost engine that provides good power while meeting Tier II emissions with fuel consumption that gets closer and closer to V-6 engines,” FEV’s Tomazic sums up.

Bottom line: This delightfully satisfying pushrod V-8 simply gets it done.