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Country of origin:United States
Produced from:1974 - 1976
Numbers built:12
Internal name:C3
Designed by:John Greenwood
Author:Wouter Melissen
Last updated:November 20, 2014
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Click here to download printer friendly versionFrom the late 1960s, John Greenwood had successfully raced relatively standard Corvettes in national and international events. A key ingredient of the Greenwood success was superior engine tuning; his big block V8s could run at 8,000 rpm while most others would blow up at anything over 7,000. Campaigning the C3 Corvette for several seasons did reveal several chassis flaws, which Greenwood addressed with an altogether more extreme 'Wide Body' Corvette competition car launched early in 1974 at the North American International Auto Show in Detroit.

Unlike his previous racers, which used production-based chassis, the new-for-1974 Corvette boasted a bespoke tubular frame. Built by Bob Riley's Protofab, it still used the centre section of the production chassis but with heavily revised front and rear frames to accommodate Greenwood's revised suspension geometry. The biggest changes were at the rear end where the traditional swing axle and transverse leaf spring setup was replaced by double wishbones with coil springs and adjustable shock absorbers. Riley also assisted in properly setting up the new chassis.

The new IMSA Corvette was powered by the latest specification Greenwood tuned big block V8. Compared to the production 454 ZL1, the all-aluminium unit featured a slightly larger bore to bring the displacement up to 467 cu in (7,654 cc). All major components like the pistons, camshaft and crank were replaced by competition-specific parts to ensure they could cope with the added stresses. A dry sump lubrication system was also fitted as was Greenwood's own magnesium cross ram intake setup that used the Lucas fuel injection internals. Running on high octane gas, the heavily modified ZL1 V8 produced around 700 bhp.

Greenwood's efforts had not gone unnoticed at General Motors and for the development of the all-new body, he received backdoor assistance from the likes of legendary engineer Zora Arkus-Duntov, who is generally considered the father of the Corvette. The most striking features of the new design were the very wide fenders, which were filled with massive wheels and tyres. In order to generate additional downforce the fenders were angled steeply angled at the leading edge. They also featured rear openings to help lower the pressure inside the wheel wells and reduce lift. Additional downforce was created by a relatively modest rear wing.

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  Article Image gallery (65) Chassis (6) Specifications