Cummins’ Kyle Richardson provides an overview of the company’s latest technolog at TMC’s 2026 Annual Meeting in Nashville, Tenn. (Seth Clevenger/Transport Topics)
March 23, 2026 3:35 PM, EDT
Key Takeaways:
- Cummins’ EPA 2027 X15 features a larger two-piece SCR system to meet lower NOx limits while keeping overall system weight neutral.
- The engine is rated up to 605 horsepower and 2,050 pound-feet of torque and is expected to deliver 4% fuel-efficiency savings.
- Advanced analysis-led design allowed Cummins to offset added aftertreatment hardware without increasing engine weight.
NASHVILLE, Tenn. — Cummins unveiled its EPA 2027-compliant X15 diesel engine at the Technology & Maintenance Council Annual Meeting, emphasizing a redesigned, larger SCR system and fuel-efficiency gains.
The engine is rated up to 605 horsepower and 2,050 pound-feet of torque.
“The aftertreatment system is clearly bigger. We went to a larger SCR catalyst because [of more nitrogen oxide] reduction, so you have to have more surface area. And so we needed more substrate. And so that weighs more. But overall, at a system weight level, it’s neutral,” Director of Customer Support Mark Ulrich told Transport Topics at the conference.
EPA is set to leave in place a Biden-era requirement that NOx emissions for heavy-duty trucks drop to 35 milligrams per horsepower-hour from 200 mg/hp-hr.
As a result of the increase in size and NOx emission requirements, the SCR is now built from two parts, Principal Product Manager Kyle Richardson said during a March 17 TMC briefing.
“We evaluated multiple options for hitting that lower NOx target. We’ve selected what we think is the best solution for our customers for all those different attributes,” Ulrich told conference attendees. “So, we have a heated aftertreatment system. It has a motor generator that provides the power. There’s grid heaters in the aftertreatment system. Those grid heaters are a simple technology that’s been used for many years in different kinds of applications.”
The aftertreatment unit has a dedicated 48-volt alternator for the heaters. There is one heater before the diesel oxidation catalyst/diesel particulate filter and one before the SCR segment.
The engine isn’t any heavier, Cummins executives were keen to stress.
Cummins was able to offset the larger aftertreatment hardware through advances in analysis-led design, using modern engineering tools to remove material where it wasn’t needed while maintaining strength. “You can sculpt the block,” Ulrich said, adding that iron is used only where required structurally.
“This is not the first time we’ve ever done this. We did it with a prior-generation [X12] engine … which will be going out of production at the end of this year,” he told TT. “That was the first time we had a sculpted block. And it’s a really robust design. So, that allowed us to achieve the weight savings on the engine.”
Fuel-efficiency improvements were not ignored, as is the case with many original equipment manufacturers’ newest engines.
Patrick Brennan of Cox Fleet talks about the common missteps that fleets make in planning for future maintenance and operational needs. Tune in above or by going to RoadSigns.ttnews.com.
Lyndon Jones, vice president of North America sales and customer support, told TMC attendees the 2027 X15 was designed to give fleets stronger performance and greater fuel economy without adding unnecessary complexity.
Cummins previously told TT the engine would offer 4% fuel-efficiency savings for fleets.
The debut was somewhat belated after Cummins said in August it would delay the launch of its EPA 2027-compliant X15 due to uncertainty around the introduction of the federal tailpipe regulations.
But with greater clarity emerging on the regulations — the final details are expected before the end of the month or early in April — Cummins unwrapped the 2027 X15 for the first time.
The first version of the X15 was introduced in 2016 ahead of the launch of 2017 EPA greenhouse gas and fuel-efficiency standards. The X15 replaced the ISX15, which was produced between 1999 and 2020.
Cummins’ diesel X15 is one of six EPA 2027-compliant engines Freightliner and Western Star will offer.
Kenworth’s recently unveiled C580 heavy-haul tractor and truck will come with the X15 as standard. The C580 is the replacement for the C500 model.
