A pair of truck manufacturers are about to breach the wall that has confined four-cylinder diesel engines to smaller commercial-duty truck classes.

Fuel-efficiency demands and tightening emissions regulations will lead to the replacement of six-cylinder diesel engines with a new generation of bigger, tough four-bangers, said Shaun Skinner, president of Isuzu Commercial Truck of America, which is about to launch a new four-cylinder delivery truck.

Companies deploying four-cylinder engine trucks in their delivery fleets say they are achieving fuel savings with no loss of performance or complaints from drivers.

“We had some trepidation, but the drivers were happy with the first two we bought,” Gregg Hodgdon, fleet manager for E.A. Sween Co., a Minnesota-based preparer and distributor of sandwiches to stores in 26 states, told Trucks.com.

Freightliner Trucks is also eyeing the greater use of four-cylinder engines in trucks.

A spokesman for Daimler Trucks North America, which owns Freightliner and engine builder Detroit Diesel, said the company won’t be ready to discuss its plans until later this year. But the automaker introduced a new Daimler-built four-cylinder engine at the Work Truck Show in Indianapolis in March. It said at the time that the engine would be available for certain Class 6 Freightliner delivery trucks by the end of the year.

Other truck engine builders, though, insist that they are sticking with six-cylinder engines for Class 6 and larger trucks.

“We don’t offer four-cylinder engines” said a spokesperson for Navistar, owner of International Truck and Engine Corp., when asked whether it has any plans to move into that category.

Likewise, Cummins Engine, one of the world’s largest diesel engine manufacturers, “does not envision a convincing rationale for introducing a four-cylinder engine to the medium-duty and vocation truck market in North America in the near future,” said Kevan Browne, a company spokesman.

Cummins says its six-cylinder diesels provide greater durability in urban-duty use and believes drivers prefer the “smoother, faster acceleration” of the bigger engines, Browne said.

But Isuzu, which is reentering the Class 6 market in the U.S. next year after an eight-year absence, says the time is right for engine downsizing.

“We looked at population trends and the growth is in cities, and that’s where it will continue to grow,” Skinner said. “We targeted the truck to be an urban delivery vehicle and we felt that a four-cylinder made great sense because it drives down the cost of operating, the cost of fuel and in some cases, the initial purchase cost as well.”

The new Isuzu engine, the 4HK1, is a 5.2-liter in-line four-cylinder, turbocharged diesel.  It is a version of the 4HK engine Isuzu uses in its class 3 to 5 trucks throughout the world.

There is a perception among drivers that sixes are better than fours in delivery trucks, as Cummins’ Browne argued. But several fleet managers who use four-cylinder Isuzus said the transition from the company’s six-cylinder models was pretty painless.

“A lot of our guys rolled their eyes” when Abt Electronics announced it was moving to Class 5 trucks with four-cylinder engines, said Chuck Metoyer, who managers the Midwestern consumer electronics and appliance retailer’s 450-truck fleet.

But drivers testing the first of the four-cylinder trucks quickly changed their minds, he said.,

The move came when Isuzu withdrew from the Class 6 segment in 2009 as its partnership with General Motors dissolved in the GM bankruptcy. GM had supplied the truck chassis.

Abt purchased four Isuzu delivery trucks with four-cylinder engines and quickly found “that the drivers had no problem,” Metoyer said. “They say they don’t feel all beat up at the end of the day from engine vibration, and they’re more comfortable.”

Most Abt deliveries involve relatively light-weight but bulky material, “so our need was for space more than power, but we got both with the new trucks.”

Now the company hears more complaints about a lack of engine power from drivers using its six-cylinder trucks than those in the fourbangers, he said.

Abt, which is headquartered outside of Chicago and delivers throughout Iowa, Michigan and Indiana as well as Illinois, now has about 175 Class 3 through Class 5 trucks with four-cylinder engines.

Metoyer plans to test Isuzu’s FTR Class 6 delivery truck when it goes on sale next year.

Sandwich company Sween reported much the same experience when transitioning from six-cylinder to four-cylinder delivery trucks in 2010.

Sween’s Deli Express unit now has 150 four-cylinder Isuzu Class 5 trucks, “and we run them everywhere,” including in the Rocky Mountains, Hodgdon said.

“There’s been no kickback from the drivers,” Hodgdon said. “The only problem was in the mountains, they were a little weak in high altitudes, but we live with that.”

The four-cylinder trucks in the Deli Express fleet are averaging 13 miles per gallon while the fleet’s six-cylinder trucks get 8 to 9.5 mpg, Hodgdon said. With $2-a-gallon diesel, that’s a savings of almost 7 cents a mile on fuel alone.

Abt’s Metoyer reported a similar gain of 3 to 4 mpg for his fleet’s four-cylinder trucks over its six-cylinder models.

As for driver concerns about engine displacement, “I don’t think 90 percent of the drivers will know the difference,” Hodgdon said. “If the truck does the job, they don’t care about the engine size.

That’s been Skinner’s mantra as he prepares to market the new Isuzu FTR trucks.

“We are going to be leading the industry down this path,” he said. “People don’t really need all the horsepower and torque they’ve been told they need, especially in the urban areas.”

Isuzu hasn’t disclosed power specifications for the U.S. version of the 4HK1 engine it will be using in the FTR. It likely will be tuned to produce more power than the 215-horsepower, 452 foot-pounds of torque version used in its smaller Class 5 trucks, said Skinner.

That compares with a range of 200-325 horsepower and 520-750 foot-pounds of torque for the  market-leading six-cylinder diesel engine for medium-duty trucks, the 6.7-liter Cummins ISB6.7.

Cummins spokesman Browne said there “is a role” for four-cylinder, medium-duty truck engines in the U.S., but only in specialized applications.

Skinner, however, believes that increasing demand for better fuel efficiency and lower emissions levels will drive the industry toward greater use of four-cylinder engines.

Silpa Paul, a transportation industry senior analyst with the international consulting firm Frost & Sullivan, agreed.

She said she doesn’t foresee widespread adoption of four-cylinder engines for heavy-duty trucks of 32,000 pounds GVWR and greater in North American anytime soon. But regulatory and economic demands, Silpa said, have four-cylinder engines “poised to soon become the norm in medium-duty applications.”

Watch:

Isuzu unveils new FTR truck at the Work Truck Show

About The Author

John O'Dell

John O'Dell is a Trucks.com contributing writer, green technology expert and editor of TheGreenCarGuy.com. He previously wrote for Edmunds.com and the Los Angeles Times, and served on the National Research Council committee that authored the seminal report “Transitions to Alternative Vehicles and Fuels.”