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Two X15 Engine Series. Two Gearing Strategies

The X15 Efficiency Series and X15 Performance Series engines for 2017 have recently been launched, to great interest within the trucking community. These two X15 engines share a large number of components, from the block to the Electronic Control Module (ECM) to the new Single Module™ aftertreatment system, as well as advanced diagnostics and the capability for over-the-air calibration. At the same time, each engine has a different power cylinder recipe, with unique horsepower and torque curves, and is optimized to exceed the expectations of customers with different needs. Proper spec’ing will help ensure that your customers meet their operational objectives.

The Efficiency Series is designed primarily for customers with linehaul and regional-haul operations focused on lowering total cost of operation by maximizing fuel economy. It produces the best results for fleets with average speeds of 35 mph or above carrying average loads in the 65,000 lb-to-80,000 lb range. However, the engine is approved and able to deliver great fuel economy for customers hauling up to 145,000 lb.

The Performance Series is a better choice for heavy-haul fleets and vocational trucks, delivering the power and torque needed to enhance low-speed maneuvering on mountainous terrain or in off-highway operations. It can be spec’d for trucks hauling as much as 185,000 lb. For applications with a higher gross combined vehicle weight (GCVW), you and your customers should contact Cummins for specialized heavy-haul assistance.

A key element to ensuring driver satisfaction with these engines is making sure that your customers get the right gearing using version 6.2 or higher of PowerSpec.

X15 Efficiency Series Gearing Recommendations
The chart below outlines the three gearing setups, ranging from a balanced approach with stronger performance characteristics to one that achieves maximum fuel economy, based on the resulting rpm at desired cruising speeds.

Because the X15 has the highest compression ratio of any engine in the industry, we’ve been able to lower the operational sweet spot to 1100 rpm while delivering up to 1850 lb-ft of peak torque on the Efficiency Series. As a rule of thumb, downspeeding by 100 rpm equates to a 1 percent to 1.5 percent gain in fuel economy.

Customers who choose the maximum fuel economy gearing must spec an automated manual transmission (AMT) in order to avoid excessive driver shifting with a manual transmission. Customers choosing to gear for fuel economy with a target cruise speed in the 1250 rpm-to-1350 rpm range will have the option of either an AMT or manual transmission.

Obviously, the higher GCVW, the more horsepower and torque that will be recommended. Gearing the X15 Efficiency Series for balanced operation in the 1350 rpm-to-1500 rpm range is ideal for performance-oriented customers (hauling up to 85,000 lb) who also want better fuel efficiency but need strong pulling power. Fleets exceeding that load and spec’ing the X15 Efficiency Series engine should add 200 rpm to all the recommended gearing ranges outlined above, or opt for the Performance Series engine.

X15 Performance Series Gearing Recommendations
Customers who run line-haul or heavy-haul trucks with loads up to 185,000 lb should be steered toward the X15 Performance Series engine. It’s also the best choice for vocational trucks such as cement mixers and large dump trucks that need the power of a big-bore, heavy-duty engine. Customers who often drive in muddy construction sites and up steep ramps with a full load will benefit from the X15 Performance Series because it provides the power needed for low-speed maneuvering. Heavy-duty fire and emergency vehicles should also be spec’d with an X15 Performance Series engine.

As you can see from the chart below, gearing for performance-oriented vehicles is recommended in an rpm range from 1300 rpm to 1700 rpm. This provides greater pulling power and acceleration. For customers in vocational applications, add 100 rpm to the recommended gearing ranges.

Customers can choose from among performance, balance or fuel economy setups based on their fuel-economy objectives, driver preferences and duty cycles.

A New Version of PowerSpec® for the New X15 Engines
Cummins has released an updated version of PowerSpec that will help you and your customers get the ideal gearing (and set up all of the programmable parameters) on 2017 X15 Efficiency Series or Performance Series engines. Visit to experience how easy Cummins is making it to get the best gearing recommendations and spec’ing advice for your customers.

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