It took countless calculations, 15-hour school days and a 2,500-mile road trip by a group of intrepid parents, but the Shop Girls unpacked a scratch-built car on the floor of the George R. Brown Convention Center that makes the Prius hybrid look like a Mack truck.

“I never thought I’d actually use angle identities in real life,” says Maia Hanson, a junior at Granite Falls High School in Washington, as she explains the tricky process of programming the chip for the transmission in Iron Maiden. The super-efficient, diesel-powered one seater joins entries from colleges and high schools around the country at Discovery Green this weekend in the Shell Eco-marathon.

Started in 1939 as a friendly bet between two scientists at the oil company to see who could squeeze the most mileage from their cars, the event has evolved into a contest that draws hundreds of budding engineers to competitions on three continents.

For the first time in Houston, the American contest kicks off today at 9 a.m. when teams take test runs around the park, and the convention center opens up to eco-curious Houstonians. The opening ceremony takes place at 9 a.m Saturday, followed by races until 8 p.m. where vehicles with gas tanks the size of Coke cans drive a set distance around the course and see who can burn the least amount of fuel in the process.

After an outdoor showing of Apollo 13 in the park, competition resumes Sunday morning and ends with an awards ceremony at 6 p.m.

Local favorites include two teams from the University of Houston and a car from Lamar University in Beaumont. Fuel types vary from hydrogen to biofuels, and entries fall within categories for “prototype” and “urban concept” vehicles, which are slightly closer to street legal.

Hanson and the eight other young women on her team approached the challenge by subjecting foam models to a wind tunnel, then designing everything to fit inside the most efficient shape. The result looks like a fiberglass rocket set atop three bicycle wheels with a 4.5 horsepower Yanmar motor in the back. The Shop Girls’ male counterparts, who go by the team name Urban Autos, toiled beside them on their urban-concept entry shaped a more like a miniature coupe from the 30s.

Shell representatives say a few teams in the past have garnered patents for their inventions and a number of participants go on to successful careers in engineering. For Hanson, though, seeing their creation take its first laps around the school last Saturday was reward in itself.

“We’re kind of used to having automatic gratification, and this has been the work of eight months,” she says. The team hopes the weekends and late nights of tweaking at the school over the last few weeks will pay off as they take to the streets of downtown Houston this weekend.