General Motors Co. will unveil at the New York auto show later this week an extra-efficient version of its new-for-’11 Chevrolet Cruze compact car that relies heavily on aerodynamic tweaks to achieve a highway rating of 40 mpg (5.9 L/100 km) with a manual transmission.

Available in the fourth quarter, about the same time regular units begin shipping to dealers, the Cruze Eco comes with the car’s up-level 1.4L turbocharged Ecotec 4-cyl. engine featuring variable-valve timing.

The Flint, MI-built 4-cyl. is mated either to a 6-speed manual or 6-speed automatic transmission in the Cruze Eco.

GM expects segment-leading fuel economy, although city-cycle numbers will not be revealed until closer to launch. GM also will disclose at that time fuel economy numbers for Cruze Eco models equipped with the available automatic.

“The Cruze Eco delivers hybrid-like efficiency without the price tag,” Jim Campbell, vice president-Chevrolet marketing, says in a statement. Pricing will not come until closer to launch.

GM says the Cruze Eco achieves its 40-mpg highway mark with a number of aerodynamic additions, such as a lower front grille air shutter designed to close at higher speeds.

The Cruze Eco also receives more “close-outs” to its upper grille, and a lower front air dam, as well as extensive use of underbody panels and a rear spoiler to further enhance aerodynamics.

GM lowers the ride height slightly and installs lighter-weight, 17-in. aluminum wheels and ultra-low-rolling resistance tires from Goodyear Tire and Rubber Co. The axle ratio on manual-transmission models also is optimized for fuel economy.

GM made similar enhancements to the Chevy Cobalt, which the Cruze replaces, and the Chevy Silverado, shortly after fuel prices spiked two years ago.

The Cruze combines with the Chevy Volt extended-range electric vehicle for a one-two punch later this year from GM, which after 2009’s bankruptcy intends to shift its focus away from big pickups and SUVs to more economical passenger cars and cross/utility vehicles.

The two cars also represent key plays for GM as it works to meet future fuel-economy rules of 35.5 mpg (6.6 L/100 km) by 2016, standards that begin stepping in next year.

GM will build the Cruze at its Lordstown, OH, assembly plant, which recently received a $350 million investment to support production of the Cobalt replacement.

Chevy also shows at New York a Cruze with an RS appearance package, which GM will make available on LT and LTZ trim levels.

Cruze RS models receive unique fascias, as well as design tweaks to their rocker moldings, rear spoilers and fog lamps.

Inside, an up-level instrument cluster for the package includes chrome accent rings in place of standard silver finishes and opaque cluster bezels, allowing ice-blue backlighting to shine through for a sportier appearance after dark.

In addition to the 1.4L, the Cruze will receive a normally aspirated, Toluca, Mexico-built 1.8L 4-cyl. engine as standard equipment on LS-trim base models.