1971: Gear fast, run slow

October 5, 2010  | by: Max Heine

The gear fast, run slow approach to engine design was a natural evolution after turbocharging came along with its ability to allow the engine to produce more power at a lower rpm. Exploiting continual improvements in the injection system and the ability of the turbo to jam more air into the cylinders, it paved the way to fuel savings.

The technology was developed by Robert Deal at Signal Deliveries, a contract carrier started up by Leaseway Transportation, in conjunction with Detroit Diesel Corp. At the time, the engine governor was used to limit road speed, meaning the engine ran at 2,100 rpm if the driver used maximum throttle. Deal, who later earned the CCJ Career Achievement Award, reasoned that slowing the engine down by using faster axles but still cruising at the same speed would save fuel via better turbo performance, reduced engine friction, and easier, better breathing.

Instead of cruising at 1,900 rpm or higher at highway speeds, the axle ratio was chosen so the engine would cruise at 1,600 or even less. A Detroit Diesel engineer  designed a governor that caused the torque to rise gradually as rpm dropped below 2,100 so the engine would deliver plenty of power and feel good, even  at the lower cruise rpm. A 4.11:1 axle ratio might be replaced by a 3.70:1 or lower ratio.

Detractors who were used to un-turbocharged engines argued that injectors would clog from carbon deposits. But the additional air supplied by the turbo because of the governor’s action, and ever-improving injection systems, ensured clean combustion and the problem never appeared.

Gear fast, run slow required driver discipline or the use of separate road speed governors so cruise speed would not be increased. But the process worked, changing forever the way trucks were geared and saving untold millions of gallons of fuel.


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