HAGA-GUN, Japan - Who says gasoline engines have reached their limit? A race to seek out the best mileage is out to prove that when it comes to frugal driving, a 50cc motorcycle engine can go a long way.

In the annual Eco-Run event, sponsored by Honda Motor in Japan, contenders design vehicles powered by a four-stroke 50cc engine, driving them seven laps around a track for a total 16.8 km (10.4 miles) using as little fuel as possible.

Apart from a few regulations on the vehicle's dimensions -- they must measure under 3.5 meters (12 ft) long and have at least three wheels, for instance -- the rules are simple: cover the designated distance in under 39 minutes and 20 seconds, equivalent to a minimum speed of 25 km (15.5 miles) an hour.

The mileage is calculated based on the amount of petrol consumed.

The record so far is a mind-boggling 3,435 km/liter (8,080 miles per gallon), set in 2001. On that machine, traveling the circumference of the earth would require just 12 liters (3.2 gallons) of fuel.

In the first race, held in 1981, the winner clocked 292 km/l.

It's the ideal type of race -- perfect for our generation, said Honda's chief executive, Takanobu Ito, who made the trip to the Motegi circuit, in northeastern Japan, to watch the finals.

Under a clear blue sky on Sunday, more than 300 teams, divided into junior high, high school, college-level students and the rest, participated in the race, with helmet-wearing drivers squeezed into the hand-made machines.

The vehicles came in a myriad shapes and forms, from the rudimentary, low-cost variety using cardboard boxes and cheap bicycle tires to the sleek, sophisticated machines cloaked in the latest lightweight material built by professional engineers.

We used plastic cardboard because it was easy to shape, said Tomoaki Ihata, the 14-year-old driver of the team that placed second in the junior high school category.

One of the keys to getting good mileage is to switch off the engine without disengaging the accelerator, he said.

His team's performance of 780 km/l, however, was no match for the black, tadpole-shaped glider designed by Mineyasu Oana and his team of Honda engineers, who would have nabbed a consecutive trophy with a result of 3,262 km/l had they not been disqualified for crossing the finish line 2 seconds too late.

This was the perfect year to go for the record, said a disappointed Oana, whose day job is to improve the aerodynamics on Honda's jet engine aircraft.

We had some wind today, so that would have given us an advantage, he said between apologies, noting that his team had worked out an ideal body form through sophisticated mathematics, not to mention improvements to the engine by seeking out the best fuel injection cycles.

Too bad we miscalculated our time. But we'll be back next year.

(Editing by Miral Fahmy)

Japan