Detroit Unveils Gen 6 Heavy-duty Diesel Lineup

March 13, 2026

Matt Wolfe

Detroit’s Gen 6 engine family was revealed at the company’s engine production facility in Michigan just outside of Detroit. (Daimler)

Detroit has introduced its Gen 6 heavy-duty diesel engine family. Comprised of the DD13, DD15 and DD16 engines, the Gen 6 aims to be fully compliant with the EPA’s 2027 emissions standards by utilizing proven, reliable technology. SAE Media was on hand for the reveal of the Gen 6 lineup at Detroit’s engine production facility in Michigan just outside of Detroit.

“Freightliner and Western Star customers depend on Detroit to operate reliably, efficiently and powerfully, and we’re honored by the trust placed in both the Detroit brand and the DD13, DD15 and DD16 engines to help navigate past transitions as well as this next one,” said David Carson, senior vice president of sales and marketing at Daimler Truck North America. “With our Gen 6 engines, we have a successor that builds on years of proven performance to be prepared for ’27 and beyond.”

Detroit’s Gen 6 engines are largely a refinement of the current generation’s design. However, the tweaks Detroit engineers have made to the new engines result in greater efficiency and compliance with upcoming EPA regulations.

The Gen 6 12.8-liter DD13 engine offers 410-525 hp (kW) with a torque rating of 1450-1850 lb-ft (Nm). The middle sibling 14.8-liter DD15 can serve up 425-505 hp (kW) and 1,550-1,900 lb-ft (Nm) of torque. The biggest member of the family, the 16.6-liter DD16, will be available with 560-605 hp and 1,850-2,050 lb-ft (Nm).

Technical highlights of the Gen 6 engines include a redesigned and simplified fuel system, updated turbos, a new asymmetric intake port and the use of Miller-cycle camshaft timing. (Daimler)

Technical highlights of the new engines include a redesigned and simplified fuel system, updated turbos, a new asymmetric intake port and the use of Miller-cycle camshaft timing. The pre-SCR system for the Gen 6 works in tandem with a new thermal control valve that helps the system reach operating temperature more quickly, reducing the need for parked regens.

Detroit also states that the aftertreatment design retains its existing footprint with no impact on packaging. There is also a new wastegate actuator that improves braking performance and provides greater power for high altitude conditions.

Proven performance

The design mantra that Detroit followed for the Gen 6 engine was that this iteration of its heavy-duty powertrain lineup would be based around proven, existing technology. Most of the updates are component-level changes that may seem inconsequential on their own, but add up to a cleaner, more durable powertrain package.

The Gen 6’s thermal control valve helps this engine family meet EPA ‘27 standards. (Daimler)

SAE Media interviewed Steve Collins, director of field sales engineering for Detroit, to discuss those changes in depth and what their net effect was on the overall efficiency and durability of the Gen 6 engines.

“Of course there’s benefits to using proven tech from a design, validation and development standpoint, but the customer also benefits from that approach,” Collins explained. “Even though there’s a lot of commonality and similarities across the platform, each offering is still targeted for specific applications.”

“For example, the DD13 is still mainly aimed at vocational use cases or weight-sensitive applications. The DD15 is targeted towards highly fuel-efficient line haul and long haul needs. Then in 2028, when we release the Gen 6 DD16, that’s a severe-duty vocational or heavy haul engine with high horsepower and torque output.”

Taking the heat

Detroit’s Gen 6 DD13 and DD15 engines will be available beginning in January 2027. (SAE Media)

The Gen 6’s thermal control valve is one of the notable component changes that helps this engine family meet EPA ’27 standards. “The thermal control valve really is all about managing heat for the aftertreatment system,” Collins said. “That valve can create a bit of back pressure in the system so it can maintain consistent temperatures and convert NOx efficiently.”

Collins further explained how the thermal control valve helps maintain lower tailpipe emissions in all conditions. “For high idle applications or stop-and-go applications when the engine isn’t under full load, it’s likely not producing enough heat. That thermal control valve aids and assists in those conditions to maintain heat in the aftertreatment system. The goal is to keep the truck up and running and not require a parked regen.”

Collins continued, “We’re managing temperatures differently through the thermal control valve and sometimes upstream of that component for the new engines. We’re also moving to a common EGR cooler as well so there’s a little bit more commonality between the displacements. The whole idea is to improve performance through thermal management. And really, it’s all about improving the performance of the aftertreatment system.”

Turbo time

Another subtle but notable change for Gen 6 was the use of ball-bearing turbos across the entire range rather than journal-bearing units for select engines. The ball-bearing turbo used for the Gen 6 engines is manufactured in-house by Detroit and is common across the entire engine range.

“The journal-bearing turbos were targeted towards vocational applications,” Collins explained. “We could get a little bit better thermal management out of the journal-bearing design for those vocational applications. So, knowing that and knowing that the ball-bearing design is also more efficient, we worked upstream on the thermal management requirements that the journal-bearing turbo was helping us with.”

The pre-SCR system for the Gen 6 works in tandem with a new thermal control valve that helps the system reach operating temperature. (Daimler)

Collins continued, “This is where adding the thermal control valve across the board really helped. That allowed us to move away from the journal bearing and move into the ball-bearing design across the entire platform which was more efficient. We manage the heat in different ways now, and the ball-bearing turbo also allows for quicker throttle response and spool up. This also helped us with down speeding since we were able to provide more torque at a lower rpm as well as improvements to overall throttle response.”

Fueling simplicity

The individual subsystem that saw the largest revisions for the Gen 6 engine was fuel delivery. The fuel system for the Gen 6 uses an oil-lubricated high-pressure fuel pump. Detroit already has a similar component in use for its medium-duty engines. The injection system has also been updated to a high-pressure common rail. This eliminated the need for amplified injectors as the system now has a unified pressure from the pump through the injectors, which is roughly 2,500 bar (36.3 ksi).

“Our heavy-duty platform has traditionally used a fuel-lubricated high-pressure fuel pump,” Collins said. “The oil-lubricated pump is new to our heavy-duty platform, but we’ve had an oil-lubricated pump on our medium-duty unit for years, so it’s not new technology to us.”

The fuel filter housing is a cannister style with an integrated hand pump for manual priming. This unit will be shared across the entire Gen 6 range. “We do have a heating element in the fuel filter module,” Collins explained. “The old amplified system made a lot of heat on its own thanks to the return fuel coming back from the rail. So to help our customers operating in cold conditions, we added a heater element within the fuel filter module to prevent jelling and buildup.”

According to Detroit, non-amplified injectors provide more consistent performance over their lifespan. Detroit also claims that the revised fuel system not only provides a net efficiency gain but also will be more durable than the Gen 5 design when exposed to low-quality fuels.

“Our customers can’t always control the quality of the fuel that they have access to,” Collins said. “Having a robust fuel system is a very important feature for [our customers] and adds additional value through better system durability.”

Adding efficiency

Fuel efficiency was also a focus of the Gen 6’s design. Detroit is claiming a 3% fuel efficiency gain over their current heavy-duty engines. In addition to the fuel system revisions, these improvements were achieved via better airflow management, reduced parasitic loss in the oiling system, and the use of Miller-cycle cam timing.

“Increasing efficiency is all about air and combustion optimization as well as reducing friction and pressure within the engine itself,” Collins said. “Our new cylinder head design for the Gen 6 increases intake air swirl, and combined with new fuel injectors, this improves fuel and air mixing for more complete combustion.”

Collins also discussed how Miller-cycle cam timing helps the Gen 6 achieve higher fuel efficiency. “With Miller cam phasing, we’re leaving the inlet valve open for longer during the compression stroke. That allows that compression stroke to be completed with less overall work. We’re working the engine less to complete that compression and be able to still achieve a higher static compression ratio because we’re using a smaller piston bulb.”

The lubrication system was the other area that Detroit focused on when looking for efficiency gains. “We made some changes to the oil separators. We moved from an oil-driven separator to an electronic separator,” Collins explained. “This gives us more control and better separation efficiency at low load. We combined that with a variable-speed oil pump to reduce overall oil flow and demand on the pump when full pressure isn’t needed.”

Collins explained Detroit’s strategy on how the variable-displacement oil pump is utilized. “These engines see a lot of different loads. They may be running down the highway with a full load, but they also may need to idle on the jobsite and utilize a PTO. There’s varying requirements on the oil circuit. We wanted to make sure that we had an oil pump that could supply the right amount of oil at the right pressure without overdoing it. The more pressure you add, the more efficiency you lose. But you still need to provide the necessary oil pressure for various loads.”

Collins continued, “The variable pump allows us to match the size of the displacement of the pump itself to meet the needs of the oil circuit depending on how the engine is being utilized. We can match the output perfectly to the amount of work required to supply the right amount of oil at the right time and in doing so, provide better efficiency.”

Design details

One detail that is missing on the Gen 6 engines is a 48-volt electrical system. While many of Detroit’s competitors have chosen to move to a 48-volt architecture for their new engine families, Detroit chose to forgo such a system for its EPA 27-compliant mills.

“Our biggest technical challenge with that decision was figuring out if we could manage temperatures enough without utilizing a 48-volt heater. We wanted to see if we could use the thermal control valve and move the pre-SCR chamber as close as possible to the heat source so the aftertreatment system could heat itself up quickly enough. We decided that if we could accomplish that without introducing new technology, that was the route that we were going because we think it provides the most value for our customers.”

The cooling system for the Gen 6 saw minimal but important revisions. “There aren’t a ton of changes on the cooling side,” Collins said. “There’s some internal changes to the block itself that help manage temperatures, but from a design standpoint, a lot of familiarity moving from Gen 5 to Gen 6.”

“We did add an electric heater to the thermostat unit. This is allowing us to melt the wax ahead of time within that thermostat prior to the system heating up by itself. That allows us to manage thermal energy based off map data and actual demand. We can start to pre-cool by utilizing that electronic heater on the thermostat.”

Coming soon

Detroit’s Gen 6 DD13 and DD15 engines will be available beginning in January 2027. Gen 6 DD16 production will follow beginning in January 2028. The new engine family will face stiff competition from other on-road diesel offerings, but Detroit is confident its customers will be pleased with the new engines’ durability and performance.

“We’re really building up what we’ve already been doing for more than two decades,” said Greg Braziunas, head of powertrain engineering North America. “It’s really familiar technology that we’ve made evolutionary steps with to improve efficiency and reliability, all things that our customers really demand.”