Chevrolet is aiming a pair of concept cars at the growing number of drivers in the Millennial generation, giving them a look Monday at what the outside of the coupes might look like and asking them to help design the interiors.

The General Motors Co. brand unveiled the Code 130R and Tru 140S at the North American International Auto Show in Detroit. Both offer room for four, and promise a fuel-efficient 40 mpg. Neither has an interior made and Chevrolet will seek public input on that.

John McFarland, senior manager for Chevrolet's global marketing, said its surveys found that many such potential buyers are interested in cars but aren't as interested in auto brands as much as, for example, what kind of mobile phone or computer they use.

"We want to take this initial interest and turn it into a passion," McFarland said.

The two-door, rear-wheel-drive Code 130R borrows from the look of a muscle car. The front-wheel drive Tru 140S three-door hatchback is designed as an affordable version of an exotic sportscar. Both feature a 1.4-liter turbo engine with about 150 horsepower.

If made today, Chevrolet said both cars would start around $20,000 each.

Chevrolet, like many other automakers, sees the roughly 70 million Millennials born in the U.S. between 1981 and 2000 as a growing market. Cars aimed at them that are being unveiled at the show include the Chevrolet Sonic RS, as well as Toyota's new Prius C hybrid, the Mini Roadster convertible and a turbocharged version of the new Hyundai Veloster.

To design Chevrolet's two concept cars, the automaker talked with thousands of young consumers and used that feedback to guide the way they styled the vehicles. They also helped determine what features, such as WiFi and the integration of smartphones, might be used.

Chevrolet plans to show the concepts in Detroit, at other auto shows and other places around the country to collect ideas for possible interiors. Chevrolet also plans to use social media to gauge response and determine how they might change if production versions are made.

"This is a long-term strategy," said GM North America President Mark Reuss.