“We had very aggressive weight-reduction targets on this program,” said Leonard Brohl, Lead Engineer for Closure Panels on the 2014 C7 Chevrolet Corvette, unveiled Jan. 13 at a media event preceding the Detroit Auto Show. General Motors has resurrected the Stingray name for the latest generation of its iconic sports car, which continues to be a lightweight-materials wellspring for the automaker.
The C7, which enters production in 3Q13, boasts an all-new aluminum chassis/passenger cell structure that is 57% stiffer in torsion and 99 lb (45 kg) lighter than the previous C6 steel-and-aluminum structure, said GM engineers. At the car’s world debut, GM had not yet published a production curb weight for the car. It is expected to be slightly lighter overall than the base C6 coupe's 3208 lb (1455 kg).
Besides reducing mass while increasing strength, the development team aimed to retain the Corvette’s ideal 50/50 front/rear weight distribution deemed essential for superior handling.
Compared to the C6, which uses continuous hydroformed main frame rails with a constant 2-mm (0.08-in) wall thickness, the C7’s main rails each feature five aluminum segments, including extrusions at each end, a center main rail section, and hollow-cast nodes at the suspension interface points. Each segment is tuned by varying wall thickness from 2 to 11 mm (0.08 to 0.433 in). This tailors each section’s gauge, shape, and strength properties to optimize the structural requirements for each frame section while keeping mass to a minimum.
The frame is assembled at an all-new welding shop at the Bowling Green, KY, assembly plant using a precision laser welding process that GM claims holds tolerances to about 0.001 in (0.025 mm).
Supporting the frame’s greater strength and lower weight are complementing chassis elements, including hollow-cast aluminum front and rear cradles that are approximately 25% lighter and 20% stiffer than the solid cradles used on the C6 car’s structure. The steering column support is stiffened by a factor of five compared with the outgoing car using a new thin-wall magnesium casting.
C7’s use of materials includes a standard carbon-fiber hood and roof panel, supplied by Plasan Carbon Composites’ new Walker, MI, plant. Plasan has innovative manufacturing processes that shatter previous autoclave-type processing times, getting per-part processing down to 17-min machine cycles. For more detail, read this AEI article.
The unique balsa-wood-sandwich floor construction of the C6 Corvette has been superseded on C7 by a new carbon nano-composite floor pan that is lighter while maintaining strength and stiffness, said Chief Engineer Tadge Juechter.
C7’s front fenders, doors, rear quarter panels, and the rear hatch panel are made with lighter-density sheet molding compound (SMC) than the previous generation. The door outer panel measures 1.2 mm (0.047 in) thick and the inner panel 0.8 mm (0.031 in). Combined, the body materials and their design/engineering save approximately 37 lb (17 kg) vs. the C6 body structure.
(The Corvette C7's composites program will be discussed in depth as part of a free AEI Webcast in March. Go to http://www.sae.org/mags/aei/webcasts.htm to register.)
C7 seat frames are a new magnesium structure on both the standard GT seat and the Competition Sport seat with more aggressive side bolstering.
Juechter said that the Stingray's 50/50 weight balance combined with its estimated 450 hp (335 kW) output (final SAE ratings are not yet finalized) offers the new Corvette a power-to-weight ratio that is superior to those of the Porsche 911 Carrera and Audi R8.