6 days ago
Want Better MPG Out of a Honda Insight? Install a Tiny Kubota Turbodiesel
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From cylinder deactivation to active grille shutters, carmakers go to significant lengths to increase fuel economy. What if the answer is simple? YouTuber Robot Cantina dropped a tiny diesel engine in a first-generation Honda Insight and hit the road to measure gas mileage. While the Insight was one of the most efficient cars you could buy new in the 2000s, diesel-swapping yields even better fuel economy.
Stock, the original Insight is powered by a gasoline-electric hybrid drivetrain built around a 1.0-liter three-cylinder engine. It develops 73 horsepower and 79 lb-ft of torque, which isn't much on paper, but keep in mind that the little hatchback tips the scale at about 2,000 pounds. Fuel economy was impressive when new, checking in at 53 mpg combined (48/59 mpg city/highway), according to the EPA.
But, the Insight that Robot Cantina is playing around with isn't stock, and hasn't been for quite some time. After running a single-cylinder, 212cc Predator engine, it's now fitted with a three-cylinder, 719cc Kubota diesel rated at 20 hp when left stock. That's the same engine you'd find in a small yard tractor, among other applications. The triple is fitted with a turbo and linked to a Saturn-sourced five-speed manual.
Robot Cantina measured fuel economy by draining the fuel tank, weighing the amount of diesel in it, pouring it all back in, taking the car out for a drive, draining the tank again, and weighing what's left. At the beginning of the test, the Insight was carrying about 12.8 kilos (around 28.2 pounds) of diesel. At the end of the test, it had burned through roughly 2.8 kilos (approximately 6.1 pounds) of diesel. Convert pounds to gallons, factor in the distance driven, and we can easily figure out the effect that diesel-swapping an Insight has on fuel mileage.
The Insight returned precisely 70.1 mpg, which is well above the official EPA numbers and much better than most new cars. For context, Robot Cantina performed the same test with a stock Insight and logged 62.7 mpg. However, he notes that the fuel economy crown belongs to an earlier Insight-based build that was powered by a supercharged diesel engine. That drivetrain returned 78.6 mpg, which is more than a little unexpected. The turbocharger uses exhaust gases, which is waste energy, to generate boost. In contrast, the engine spins the belt that generates a supercharger's boost, so you'd think that the blower's additional power would come at the expense of gas mileage.
Robot Cantina isn't done tinkering with his Insight. Next, he wants to try out a turbo from a Volkswagen Lupo, a turbo from a Smart ForTwo, or both. In the meantime, he's proven what many Europeans figured out decades ago: Small diesel engines return stellar fuel economy.
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