Read time: 7 mins

Originally published in PowerTorque

The X15 has become the go-to engine for many truck buyers in Australia and PowerTorque takes a look at the the next step for Cummins, the Euro 6 X15, coming into the supply chain last year and ramping up this year.

There are going to be plenty of diesel engines powering heavy long distance trucks for some time to come, and one of the most important engines in the future for the Australian truck market is going to be the next generation X15 from Cummins.

Over the past twenty years the Cummins brand has come to dominate the Australian truck market and the engine which has led the way for the brand is the 15 litre, which is almost the default engine chosen for heavy duty trucks in this country, where there is a choice for the truck buyer.

The reputation of these Cummins engines has come through some tough times, but it has been the organisation itself which has carried the brand through to the place the big red engine has in the hearts and minds of the trucking people of Australia.

Iterations of the 15 litre engine, leading to the current and future X15 models, have become more and more sophisticated and better able to handle the demands of trucking in the 2020s, while, at the same time, retaining that unmistakeable Cummins ‘feel’ for the driver.

It is an intangible thing, but there is something about driving a big truck with a Cummins engine, a quality to the response, the spike of the torque, which puts a smile on the driver’s face. Over the years, as exhaust emissions rules have changed the engineering, and introduced an array of new technology, that secret sauce has not disappeared. That smile remains on the driver’s face.

Cummins has decided to go down the route most of the truck makers are also taking, that is, to move technology on to the Euro 6 exhaust emission levels even though ADR 80/04, which is planned to mandate these lower levels of particulate matter and nitrogen oxides, still doesn’t have an implementation date, despite nearly ten years of preparation for the new regulations.

“Our customers are asking to go to Euro 6, because their customers are asking them to have Euro 6 products,” says Mike Fowler, Cummins Director and General Manager On Highway Asia Pacific. “We think we’ve got a pretty good
solution for them.”

By moving to the cleaner engine now, Cummins gets access to the state-of-art technology which is used in its engines where the Euro 6 rules are in place. Using these new developments gives truck buyers access to improved performance and efficiency, plus improved connectivity with other truck systems, remote diagnostics and monitoring.

The bright red Cummins family will now include two new members, those from the X15 Efficiency Series and the X15 Performance Series. The names are a clear indication of what engine buyers can expect from each product. Although they will look similar there are clear differences between the two, in terms of hardware and software, and they are not interchangeable.

“The Efficiency Series is for the linehaul operator who cares deeply about maximising fuel economy,” says Mike.

“We have managed to do that without any performance trade-offs, it’s with some pretty innovative feature like Hill Climb Assist and some bespoke ratings.

“The Performance Series is more for the operator who needs flexibility, it might be a road train today, a B-double tomorrow, a manual transmission, a tipper and dog, any sort of vocational applications. Something with ultimate versatility in application.”


All of the new engines will include a new wastegate turbocharger, the air management on the new engines has been simplified and there is no need to fit a variable geometry turbo, something which can be expensive to maintain.

There have been further power cylinder improvements which minimise lube consumption and uses a new outside diameter biased liner, which reduces wear between liner and block. Parasitic losses are also reduced with the fitting of a more economical water pump design, plus losses are reduced with improved seals.

The XPI fuel pump system has been upgraded to improve durability. Drivetrain integration improvements between the X15 and other components, by using a new engine control module (ECM) and
software makes for better fuel economy and drive-ability.


Operators can expect a five percent improvement from the Efficiency Series engines compared to the Euro 5 X15. The engine management system is designed to enable engine down speeding, running at lower rpm levels and saving fuel. Combustion has been optimised by the use of the new turbo and a different, higher, compression ratio.

This engine will only be compatible with a drivetrain including an AMT. The drivetrain integration of control systems provides the high level of data flow necessary for the engine management systems to access the efficiency gains. The target rpm at cruising speeds is 1350 to 1450 rpm.

“We’ve gone to great lengths with our forecasted fuel use,” says Mike. “So much so, that the algorithms in our software are actually tuned to the specific gravity of fuel in Australia, which is different to that in North America. We are within two percent accuracy on all duty cycles.

“One of the pushbacks is that we do dose with a high percentage of adblue. It can be as high as nine per cent in some applications. We deliberately did the adblue vs fuel economy trade-off and by not running EGR. We can get an incremental five per cent out of the engine, but go from four to nine per cent adblue.

“On a litres of fluid basis it’s probably about the same, but adblue is a third of the price of diesel. We have designed that adblue trade-off to match the carrying capacity of the adblue tanks on a typical truck. we want to make sure the truck’s got enough adblue on board to get from Melbourne to Brisbane for example.”

Engine braking on the Efficiency Series is improved across the full rpm band on the new engine. The largest increase in retardation is in the mid-range from around 1400 rpm to over 1700rpm. The engine will be governed to 1800rpm and will be suitable for rear axle ratios between 3.21:1 to 3.9:1. The 14.9 litre engine will weigh in at 1327kg and the after-treatment at 85kg (less than 40kg higher than the Euro 5 system).

The Efficiency Series will come in two horsepower ratings 550 hp (405kW) and 580hp (427kW). Torque on both engines is up at 2050 ft lb (2780Nm), seating the two engines in what many believe to be the sweet spot for fuel economy in B-double line haul applications.


The Performance Series is clearly aimed at all of the other heavy duty transport tasks not catered to directly by the Efficiency Series models. This is the engine which will be fitted from heavy road train level down through heavy haulage, livestock, B-double, all the way to the tipper and dog and other vocational tasks.

The specification sheet has wider parameters all round, indicating the flexibility this engine is designed to offer. Rear axle ratios from 3.9:1 to 4.89:1 are recommended with the option of going with shorter or taller diffs if the
application is suitable.

The engine is governed to 2000rpm and the power and torque curves closely match those in the current X15. The compression ratio is 17:1, lower than the 20:1 on the Efficiency models. Engine braking is at a higher level than the current X15, but does not have such a marked improvement as that on the Efficiency Series.

There is a much broader range of power and torque ratings with this engine, reflecting the much wider range of transport tasks it will be expects to power. There’s a 525hp (386kW) and 565hp (426kW) Performance Series engine
available, both of which have a torque rating at the classic 1850 ft lb (2508Nm). Then for those looking for the high power ratings are at 605hp (445k) and 625hp (460kW) there’s a torque rating of 2050 ft lb (2780Nm).


A major change in the X15 is in the after-treatment system. By moving away from using EGR to control emissions, the designers were able to move to a simpler turbo, but the more complex Single Module after-treatment unit.

The unit has a number of positions where it can be mounted, options being post mounted or gantry mounted, inside or outside the chassis rails of the truck. The unit includes both an SCR unit and a Diesel Particulate Filter, which includes a diesel oxidation catalyst and a catalysed soot filter.

The unit controlling the SCR dosing system is now included in the ECM, which monitors the process with a series of sensors looking at exhaust gas temperature pressure, as well as NOx and PM levels. All of this comes in a package
about the same size as that on the current X15, but weighing more.

The engine maintenance regime for the new engines are expected to reduce overall maintenance costs for the operator and have been validated in long term field testing. Cummins have been able to push out oil drain intervals to quite a degree to reduce costs.

Cummins expect DPF life to be considerably extended in the new engines. The DPF monitoring on board will indicate when ash build-up is becoming critical and Cummins will be recommending the use of ReCon DPF exchange units.

Of course the change to a simpler wastegate turbo will reduce the need for any turbo replacement and Cummins no longer recommends any tubocharger replacement on the Efficiency Series engines.

When comparing overall maintenance costs for the new engines with the Euro 5 X15, Cummins is expecting a 24 per cent reduction in costs with the Efficiency Series and an 11 per cent reduction for the Performance Series.


“My expectation is that the split between the Efficiency and Performance Series is going to be about 50/50 for us,” says Mike. “That’s because Kenworth service a bigger diversity than anybody else. That being said I have been surprised that some of the early adopters of the Euro 6 have been people in road train operations and not the line-haul operators.”

“I think the sales of the Efficiency Series will pick up with the arrival of the Eaton Cummins joint venture Endurant XD transmission, which we are expecting later in 2022. That’s the catalyst which will get people to tick the AMT box more aggressively. Then they will be able to realise the fuel economy benefits of the Efficiency Series.”

The Cummins name has a deep respect in the Australian trucking industry and part of the engine maker’s ability to keep that reputation has been in the flexibility it has shown when presented with difficulties and changed expectations from truck buyers.

When presented to potential truck buyers, the new X15 is going to be able to tick all of the boxes for a wide range of operators and different tasks. The introduction of new technology has been tempered with a deep knowledge of all
of the issues the truck environment can throw at a heavy duty engine.

There seems to be something here for everyone from the tipper and dog operator hauling aggregate out of quarries into metropolitan construction, to the Hume Highway overnighter, from the low loader shifting over-mass equipment out to remote mine sites, to the prime mover pulling six decks of cattle out of Western Queensland.