Robert Q. Riley Enterprises: Product Design & Development

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128-mpg Diesel-Powered Sports Car

Cover of Mechanix Illustrated

Gets up to 128 mpg

Appeared in Total Recall

Gets 128 mpg

Uses Triumph

Okay to use
   the Spitfire

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Plans Include...

13 - 17x 22 in.

75-page photo-   illustrated booklet

Price... $95

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The World's Finest Plans-Built Projects

128-mpg Diesel-Powered Sports Car

Centurion 128-mpg sports car on cover of Mechanix Illustrated magazine

Featured on Cover of Mechanix Illustrated Magazine
and in the Movie "Total Recall

Centurion Turns in 200+ mpg and 250 mpg at Watkins Glen International Speedway
in NY in 2014 & 2015 (respectively) atToyota Green Grand Prix Fuel Economy Competition
& Breaks Own Record!

Order Plans Now
  - $95
Plans include thirteen 17 x 22 inch drawings & a 75 page instruction manual.

Order CenturionCenturion 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.

         One builder, however, found that our original fuel economy figures were too conservative. He has turned in 127 mpg in mixed rural and city driving.  You'll find a link to his page at the bottom of this page.

         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. 


Length: 156 inch
Width: 62-1/2 inch
Height: 44 inch
Wheelbase: 83 inch
Front Tread: 51 inch
Rear Tread: 50 inch
Brakes:  Disc front/Drum rear
Curb Weight: 1200 lbs
Ground Clearance: 6 inch
Turning Circle: 24 feet
Fuel Capacity: 10 US gallon
Seating: Two, side-by-side
Power train: Kubota #D 750 BB Diesel
Power: 17 hp @3000 rpm
Displacement: 46.5 cubic inches
Bore: 2.68 inches
Stroke: 2.76 inches

Compression Ratio: 22:1
Number of Cylinders: 3 in-line
Type: Vertical water-cooled 4-cycle
Weight: 181 lbs
Transmission: 4-speed, manual-shift, full syncro with overdrive
Final Drive Ratio: 3.98:1
Body: Foam/Fiberglass sandwich
Fuel Consumption:
   128 mpg @ 35 mph
   103 mpg @ 45 mph
    85 mpg @ 55 mph
    65 mpg in city traffic
Top Speed: 65 mph (in overdrive)
Special lubricants: Transmission filled to factory specs with Torco MTF fluid. Final drive filled to factory specs with Torco Hypoid 90 gear lube.

More information

Meet Crazy Jerry's Urba Diesel Centurion    Jerry's Centurion gets better fuel economy than the original.  To paraphrase Jerry, it makes you think the fuel gauge is broken.  You'll also find photos of an example of Centurion that looks even better than the original.  A beautiful rendition.  And you will undoubtedly enjoy the screen-grabs of Centurion in the movie,Total Recall

Driven by builder Jerry Bartlett (Crazy Jerry), his modified and optimized Centurion tied for first place at the fuel economy competition at Watkins Glen International Speedway in New York.  Fuel economy - over 200 mpg. Jerry's modifications include a further reduction of weight, improved aerodynamics, careful attention to friction throughout the vehicle, and optimizing gear train ratios. Jerry's vehicle exemplifies what can be done by careful attention to the details.
News Release:
Video from inside cabin at start of fuel economy competition.  

Essential Resources for the Do-It-Yourselfer


To Order Plans

  • Mail: Use the online Order Form to automatically calculate shipping charges and provide a total amount. Click on the "Order Centurion Plans" link above, then press "Add Item to Cart." Fill in your shipping information. Mail your confirmation page to us, along with your check, money order, or credit card information. (Outside the U.S., please make payment in U.S. funds using a credit card or International Money Order.)

  • Order by Phone: Weekdays 8:00 am to 6:00 pm MST:  623-872-8010.

                   -   Shipments to U.S. destinations go by First Class or Priority Mail (depending on weight).
                   -   Shipments to destinations outside the U.S. go by mail: "Airmail, Letter-Post."
                   -   Arizona residents, add 10.2% sales tax.

Robert Q. Riley Enterprises, LLC.
P.O. Box 12754
Chandler, AZ 85248
Phone: 602 412-7951


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