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Optimized Gearing with Cummins MidRange Engines

A great variety of vehicles use Cummins ISB6.7 engines, with tremendous variation in payload, duty cycles and customer operating preferences – everything from delivery vans and pickup-and-delivery trucks to vocational vehicles.

The key to achieving the optimal combination of fuel economy and performance for your customers is spec’ing the right engine rating for the job – and the proper gearing. Gearing that operates an engine at peak torque or power most of the time won’t result in optimal fuel economy.

isb6.7 charts june 2015ISB6.7 Applications

While each engine and vehicle will have its own set of customized specifications (developed using Cummins PowerSpec), there are two general sets of guidelines for gearing. Vehicles that are commonly used for utility trucks, step vans and pickup-and-delivery (P&D) typically are set with gearing in higher rpm ranges. Regional haul applications that carry heavier loads, such as suburban delivery and beverage distribution trucks, will typically utilize higher horsepower ratings and gear appropriately to run in a lower rpm range.

As you can see from the charts below, a typical operating range is broken into three segments based your customers’ preferences. The green bar shows the optimal settings for maximum fuel economy, the orange bar shows the gearing range for maximum performance and the blue bar shows a balanced gearing range.

The term “vocational” here is not limited to just mixers, dumps and refuse trucks that have their own specific V ratings. In this instance, vocational simply is the category that covers vehicles that are used for a lot of stop-and-go functions and operate on soft road conditions at some point almost every day, often with a varying load.

Line-haul and regional haul trucks carrying up to 33,000 lb gross combined vehicle weight (GCVW) start at 1700 rpm in the “maximum fuel economy” mode. Line-haul and regional haul vehicles carrying loads above 33,000 lb to 50,000 lb GCVW start at 1900 rpm for customers looking to minimize fuel use.

P&D trucks, utility vehicles and step vans will have gearing that starts at 2000 rpm. In all cases, the highest rpm for the ISB6.7 will be 2400 rpm, and this will be used only for customers who opt for the maximum performance setting.

So, what do you really need to remember about all of this? Just that Cummins MidRange ISB6.7 engines with higher horsepower and more torque can generally be geared to operate in a lower rpm range for better fuel economy. Your customers who desire more power and performance will need to select a higher rpm operating range. Gearing recommendations for each engine rating and application can be easily obtained by using PowerSpec, online at

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