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Cat develops spec’ing guidelines

LOUISVILLE, Ky. -- Caterpillar officials emphasized the importance of engine spec'ing during a press conference at...

LOUISVILLE, Ky. — Caterpillar officials emphasized the importance of engine spec’ing during a press conference at the Mid-America Trucking show.

Specifying an engine to perform at maximum performance levels while achieving excellent fuel economy is critical to most on-highway vehicle owners, said John Campbell, director of Caterpillar on-highway engine products.

He said that’s why the company has developed general guidelines that allow the customer to take advantage of the additional displacement and torque provided by ACERT technology to achieve the best balance between fuel economy and performance.

Many factors affect fuel economy: vehicle configuration, total vehicle weight, cruising speed, trailer type, trailer gap, tire tread depth and operator driving habits are only a few of these, according to Campbell.

“While no single gearing solution exists to balance all of these factors and meet the differing needs of truck owners, our guidelines help them develop a good spec’ing solution that will provide the best performance and fuel economy,” Campbell said.

For example, a change in traditional practice that can produce a significant fuel economy advantage when spec’ing an engine equipped with ACERT is to specify a faster (numerically higher) rear axle ratio. For example, a Cat 550 hp engine with 1850 lb-ft of torque geared traditionally at a 3.70 rear end ratio prior to ACERT Technology would achieve a certain mile-per-gallon figure running 65 mph at 1500 rpm. Caterpillar has demonstrated that the same engine and rating equipped with ACERT Technology will achieve optimum fuel economy with no noticeable loss in performance by selecting two gear ratios higher; for example, a 3.36 or 3.25 ratio.

Over the years, Caterpillar has been a pioneer in spec’ing for fuel economy, according to Campbell. “In the 1970s, we introduced 1600 rpm economy ratings, and in the 1980s and 1990s we promoted operating at a lower rpm to take advantage of the strong torque characteristics of Cat engines,” he said. “We called this approach ‘Gear Fast, Run Slow’-in other words, spec the truck’s gearing to allow it to run down the road fast, but at a slower engine speed to save fuel.

“With ACERT Technology, we can run the engine even lower in the rpm curve to achieve the absolute best fuel economy. This ‘Gear Fast, Run Super-Slow’ gearing philosophy will not affect startability or gradeability to any great degree because of the increased displacement and higher turbocharger boost pressure of the engines with ACERT Technology,” Campbell said.

While specifying the perfect component match is sometimes viewed as much an art as it is a science, truck dealer and Cat dealer sales personnel can use a computer configuration program called Design Pro to help customers construct a highly customized set of specifications to meet the fleet’s needs. Fleets can get an overview of the spec’ing process by using an abbreviated version of Design Pro on the Caterpillar On-Highway Engine Web site,

“Design Pro reflects ‘real world’ operating conditions; it is a versatile tool to compare gearing, tire sizes, aerodynamic configurations-and the effects all of these factors have on fuel economy and performance,” said Steve Brown, director of marketing for Caterpillar On-Highway Engines.

More information is available at

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