The Chevrolet Cosworth Vega is a subcompact four-passenger automobile produced by Chevrolet for the 1975 and 1976 model years. It is a limited-production version of the Chevrolet Vega, with higher performance.
Chevrolet developed the car's all-aluminum inline-four engine, and British company Cosworth Engineering designed the DOHC cylinder head. 5,000 engines were built.
3,508 cars were made. They were priced nearly double that of a base Vega and only $900 below the 1975 Chevrolet Corvette.
History
Racing origin
Known at Cosworth Engineering as Project EA, a Cosworth racing engine based on the Vega aluminum block produced a reported and powered Chevron and Lola race cars to wins in the 2-liter class in their first outings. The ZO9 Cosworth Vega engine is a de-tuned version. Bore, stroke and valve sizes are identical but it lacks the EA engine’s dry sump lubricating system (unnecessary in a street use car), has a lower compression ratio and different valve timing, and uses Bendix electronic fuel injection instead of Lucas mechanical injection to cope with a wider range of operating conditions as well as emission controls.
Development
In March, 1970 John DeLorean, GM’s general manager and vice-president, sent engine designer Calvin Wade to England in search of cylinder head technology to improve the Vega's performance. Fuel injection would be needed to control emissions without power loss; also stronger internal parts to work with the existing block and the Cosworth head. That summer, DeLorean authorized Wade to build a prototype Cosworth Vega engine. A meager budget, and resistance from managers between Wade and DeLorean, meant low priority for the project, but once approved by DeLorean it could not be killed.
In June, 1971 the prototype gave on dual Holley-Weber two-barrel carburetors. At Easter, 1972 GM President Edward Cole drove three Vegas for comparison: a base model, an all-aluminum small-block V8-powered prototype, and the Cosworth. He pledged approval from the Engineering Policy Group for DeLorean's request to initiate Cosworth production. Approval of development aimed at U.S. Environmental Protection Agency (EPA) certification soon followed, and Wade began a 12-car development program to accumulate test mileage in a range of environments including high altitude, heat and cold, to test the engine’s eligibility. At the GM desert proving ground, the car reached .
In April, 1973 the design was frozen and two cars were built to accumulate mileage for EPA emission certification. The press was notified of the program and in August 1973 a Car and Driver feature alerted the public to an upcoming Cosworth Vega. The engine needed more dynamometer time, new cam profiles to trade some high-end power for more low-end torque, and a tubular header to replace the cast iron exhaust manifold. Although delayed, the project now received higher priority, more engineering manpower and more funding. Chevrolet dealers began accepting large deposits for early delivery.
The design was frozen again in January, 1974. A stainless steel header was specified, to increase power between 2,000 rpm up and the 7,000 rpm redline. Camshaft lift and duration were eased back and the torque curve reshaped to a street-oriented peak of 5,200 rpm. Project coordinator William Large built two cars for durability testing. By April 1974, the engines ran “clean” for , after which hydrocarbon curves on the first car rose far in excess of the permitted , owing to burned exhaust valves. For certification, five months’ durability miles would have to be reaccumulated.
Development resumed, to improve emissions durability and ready the engine for more stringent 1975 standards. The fuel injection was redesigned for better air distribution. High-energy electronic ignition and mandatory catalytic converter were added; also a Pulse Air system, functionally the same as an air pump but without the pump's six-horsepower loss. A larger catalytic converter further guarded against power loss. More advanced ignition timing, and the lead-free fuel required with the converter, prevented exhaust-valve failure.
Chevrolet required all engines to survive 200 hours at full load. The Cosworth lasted over 500 hours. For a clutch burst test, Cale Wade revved the engine to 9,400 rpm under its own power without damage to clutch or engine. Three cars, in three different configurations, resumed mileage accumulation in September 1974.