Engineering the Camaro Convertible

Since its relaunch, the Camaro has had a single body style. And now the Convertible is on the street. According to the chief engineer, that’s been the plan all along.

“We left no stone unturned or piece of sheet metal unweighed,” said Chuck Russell, General Motors vehicle line director whose responsibility includes the Chevrolet Cruze compact car. He was referring to the 2011 Cruze Eco model, which, when equipped with a specially optimized six-speed manual transmission, has an EPA estimated 42-mpg highway, which is 6 mpg better than that which can be attained with a non-Eco Cruze with a manual on the highway.

Russell continued, “Our engineers were comprehensive and thorough when it came to evaluating and modifying the aspects of the car’s performance that contribute to fuel economy.”

For example, they went after mass optimization, meaning they put the car on a serious diet. After making 42 changes, the car has a curb weight of 3,009 lb as compared with 3,223 lb for a Cruze 1LT. This weight reduction exercise took a number of forms. Even removing the headrest from the center position of the rear seat.

More substantially, hundreds of weld flanges were reduced in length from 3 mm to 2 mm. Where possible, the gauge thickness of the sheet steel was reduced by approximately 0.1 mm on components.

Learnings from the Chevy Volt were applied to the Cruze Eco. Having had the Volt in a wind tunnel for in excess of 500 hours, the engineers learned several things about aerodynamic effects. So many of the things used for the Volt—more closeouts on the upper grille, a lower front air-dam extension, rear spoiler, lowered ride height, underbody panels—are deployed on the Cruze Eco. The Volt’s ultra low-rolling resistance 17-in. Goodyears on lightweight rims are used on the Cruze Eco. The tire/wheel combo weighs 36.5 lb, compared with the 41.8 lb that the standard 16-in. tire/wheel on the Cruze 1LT, for an overall weight save of 21.2 lb.

A notable, clever aero improvement developed for the Eco is a lower front grille air shutter that closes at higher speeds to improve wind flow over the front of the vehicle, yet which opens at lower speeds to improve engine cooling.

All in, the Cruze Eco has a coefficient of drag of 0.298, which is 10% better than a non-Eco Cruze.

The engine is the 138-hp Ecotec 1.4-liter turbo that is found in other Cruzes. The powertrain difference is in the gearing of the manual transmission. The gear ratios for the manual used in the conventional Cruze are (:1) first: 3.82; second, 2.16; third, 1.47; fourth: 1.07; fifth, 0.87; sixth, 0.74. For the Eco they are (:1): first, 4.27; second, 2.16; third, 1.30; fourth, 0.96; fifth, 0.74; sixth, 0.61.

Chevy’s position on the Cruze Eco is that it provides, as Chuck Russell put it, “hybrid-like fuel economy without the price.” The car starts at $18,895.