The 128-mpg Diesel-Powered Sports Car

Featured in the February 1982 Mechanix Illustrated Magazine & Featured in the movie: Total Recall

Order Centurion Plans Here   –  $95

Centurion combines diesel efficiency with lightweight construction, high engine loading, and good aerodynamics to push fuel economy well past the 100-mpg mark. Hence its name, “Centurion”, for breaking the 100-mpg barrier. The idea for Centurion was initially discarded because it was too simple. The proposal was to use an existing lightweight automotive chassis, install a high-efficiency diesel engine, replace the heavy steel body with a lightweight foam-core sandwich body, and presto: super fuel economy. But after initially rejecting the idea as too simple, we decided to go ahead with it – mainly because it was so simple. And the fuel economy techniques can work with any vehicle.

The technology used to produce Centurion’s high fuel economy is very straightforward.  An internal combustion engine runs most efficiently when it is operating at 60% to 90% of maximum output. In contrast, when an engine is throttled so it develops only a small portion of its power output capability, fuel economy plummets.

Automobiles operate most of the time with the engine throttled to 5% or less of full power, such as when cruising at low speeds in urban traffic. Even on the highway, the average family sedan can cruise at 55 mph on a little as 8 to 10 hp, which is only a fraction of the power capability of the engine. An engine throttled into fractional power regions can use double or triple the fuel per unit of power output.  It’s as simple as that.

Centurion first reduces road load by keeping weight and aerodynamic drag to a minimum with its sleek shape and low, 1,200-pound curb weight. Minimum installed power, tall gearing, and a transmission with high ratio selectivity combine to allow for high engine loading. With its 17-hp, 3-cylinder Kubota diesel engine coupled to the 5-speed transmission with overdrive in each gear, the engine can be loaded into its region of minimum brake specific fuel consumption at just about any speed. These are the primary factors responsible for Centurion’s fuel economy at cruise. Stop-and-start fuel economy benefits from low weight, which translates into less energy lost to inertia in urban traffic. Reduced fuel consumption at idle and during braking results from the small-displacement engine.

At 35 mph, Centurion delivers at 128 mpg. At 45-mph, fuel economy is 103 mpg, and at 55 mph it drops to 85 mpg. The poorest fuel economy recorded was 64 mpg, which occurred in downtown urban traffic. Turbocharging the engine would increase maximum power and performance, and improve fuel economy as well. As originally equipped, Centurion has a maximum speed of 65 mph.

Centurion is one of our most straightforward super-mileage cars because it consists mainly of an engine swap and a new body. Its Triumph Spitfire chassis is super light and relatively inexpensive if you purchase it from a wrecking yard. Total cost will be in the order of $5,000 – $7,000, depending on how the car is detailed.

Using the original Spitfire engine, instead of the Kubota diesel, could save about 50% on costs. If you would like more information on building Centurion’s body, click on One-Off Construction Using FRP/Urethane Foam Composite (Tri-Magnum is the demonstration vehicle).

Centurion was featured on the cover of Mechanix Illustrated Magazine and It appeared as a background vehicle in the movie Total recall.  Click on the images in the left margin to see larger versions. 

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