Will Next-Gen Diesel Trucks Get Bigger Engines? Expert Insights on Power, Emissions, and Displacement

The diesel truck rumor mill never stops churning. From whispers about new manufacturers entering the market to tall tales of emissions deletes becoming legal, enthusiasts love to speculate. But one of the most persistent rumors is whether the next generation of Ram, GM, and Ford pickups will feature larger Cummins, Duramax, or Power Stroke engines.

To separate fact from fiction, we consulted the engineers who designed these powertrains: Would increasing engine displacement actually make sense? Some believe bigger engines operating at lower stress could deliver more power while reducing reliance on diesel particulate filters and diesel exhaust fluid (DEF) to cut emissions. The theory suggests larger engines could produce more output without overburdening emissions systems. But as it turns out, while there’s some truth to the idea, it’s far from a guaranteed solution.

For years, Detroit’s Big Three have maintained consistent engine sizes. Ford’s Power Stroke has held steady at 6.7 liters since 2011, while Ram transitioned from 5.9 liters to 6.7 liters in 2007.5. GM’s Duramax has remained at 6.6 liters since its 2001 debut. Despite unchanged displacement, these manufacturers have dramatically increased power output. The Ford Super Duty’s original 6.7-liter Power Stroke produced 400 horsepower and 800 lb-ft of torque, while today’s high-output variant delivers 500 hp and 1,200 lb-ft—a staggering improvement.

Even more impressive? All three brands have achieved these gains while meeting increasingly stringent emissions standards. This progress is made possible by advanced aftertreatment systems, particularly selective catalytic reduction (SCR), which relies on DEF.

“If you look at our emissions level now compared to where we were 10 years ago, you know we’re not only making more power, but we’re being certified at a lower emissions level. The only way we can do that is to have a very efficient aftertreatment system. Back in the early days, when we didn’t have a diesel particulate filter on the engine and we didn’t have SCR, what came out of the engine was what came out of the tailpipe.”

— Rob Moran, Assistant Chief Engineer, Chevrolet GM Duramax

We asked Moran whether larger engine displacement would offer meaningful benefits. His response was lukewarm at best. “There’s always going to be trade-offs,” he noted. “Anytime you have fewer emissions coming out of the engine, the aftertreatment doesn’t have to work as hard. But to be honest, the aftertreatment systems today are very efficient.” Moran estimates modern systems capture 90% to 95% of NOx emissions.

Temperature plays a critical role in emissions system performance. For optimal function, these systems must operate within a precise “sweet spot” that maximizes NOx conversion without risking hardware damage from excessive heat. In this context, larger engines may not necessarily provide a clear advantage over refined, highly tuned smaller displacements.

Key Takeaways:

• Ford’s Power Stroke has used 6.7 liters since 2011, while Ram’s 6.7-liter engine debuted in 2007.5 and GM’s Duramax has stayed at 6.6 liters since 2001.
• Power output has surged despite unchanged displacement—Ford’s Super Duty now makes 500 hp and 1,200 lb-ft.
• Advanced aftertreatment systems, including SCR and DEF, have been pivotal in meeting emissions standards.
• Engineers argue that aftertreatment efficiency (90-95% NOx reduction) and thermal management may outweigh the benefits of larger displacement.