page_title: Chevrolet Opala
section_title: Development
hierarchical_section_title: Chevrolet Opala / Debut / Development
caption_attribution_description: Stock Car Brasil: the Opala 250-S engine (L6 engine) of Wilson Fittipaldi Junior's Chevrolet Opala in 1992Owner: Museu do Automobilismo Brasileiro
context_page_description: The Chevrolet Opala was a Brazilian executive car sold under the Chevrolet brand in South America from 1969 to 1992, by General Motors do Brasil. It was derived from the German Opel Rekord Series C, Opel Commodore Series A, but used local design styling and engines sourced from North America. GM manufactured about one million units including the Opala sedan, Opala Coupé, and the station wagon variant, the Opala Caravan. It was replaced by the Chevrolet Omega in 1992, also an Opel spinoff. It was the first passenger car built by GM in Brazil by the General Motors do Brasil division. A luxury version of the Opala was marketed as the Chevrolet Diplomata.
  It was used by the Brazilian Federal Police for many years. The military government issued Opalas to its agents through the 1970s. Its reliability and easy maintenance made the Opala the choice of many taxi drivers and was also popular on racetracks.
  The Opala "Coupé" continued as a pillarless hardtop well into the late 1980s, long after U.S. automakers dropped the body style.
  The Opala's long-lived 250-cubic-inch engine was also used in its replacement, the Chevrolet Omega from 1995 to 1998.
context_section_description: In the fall of 1970, a more luxurious version was added called Comodoro, reflecting Europe's Opel Commodore. The Comodoro-4 received a somewhat more powerful version of the 2.5 liter four cylinder engine in some model years, with 88 PS (65 kW; 87 hp) rather than 80 PS (59 kW; 79 hp). The same engine was used in the Opala SS-4. Even more luxurious was the Diplomata, which was released in November 1979.
  Under the hood, which hinged forwards, in the European style, the Opala originally offered only two engine choices: a 153 cu in (2,512 cc) four-cylinder and a 230 cu in (3,768 cc) straight-six. These engine were of traditional design for the era, with cast iron cylinder block and head, and overhead valves, actuated by pushrods and a camshaft mounted in the block, and pressed-steel rocker arms, whose spherical fulcrum was GM's proprietary design. Fuel was fed from either single or double-barrel carburetors. The engines had already been used for years in the USA: the 153 cu in four had debuted in the 1962 Chevy II—becoming the first inline four in a Chevrolet since 1928—and the 230 cu in six appeared in the 1963 Impala.  The 3.8 L six-cylinder was replaced by a bigger (4,093 cc or 250 cu in) version in 1971. In 1973 GM do Brasil engineers decreased the four-cylinder engine's stroke to 3 inches and increased the length of the connecting rods to 6 inches to reduce vibrations, and simultaneously increased the bores to 4 inches diameter to keep the overall displacement (2,471 cc or 151 cu in) similar to what it had been. (The bore and stroke of this Brazilian engine are exactly the same as the later Iron Duke engine designed and built by Pontiac, but the two engines are otherwise unrelated and do not share any parts.)
  The six-cylinder engine's crankshaft had seven main bearings (there were five main bearings in the four-cylinders) and the generous (if not redundant) size of its inner moving parts attributed to its durability and exceptional smoothness. The hydraulic valve lifters made for easy maintenance. The straight-six's biggest limitation through the years was poor distribution of air-fuel mixture to the cylinders due to a sub-optimal intake manifold design. Cylinders one and six (on the ends of the engine), received the lowest ratio, with a higher percentage of air in the mixture, while the central ones tended to get a richer mixture, unbalancing the engine's stoichiometric efficiency. Basically, in order to ensure the outer cylinders received a high enough air/fuel ratio to avoid detonation, the carburetor had to be set to run overly rich, which wasted fuel). This design flaw could easily be solved by installing a race intake manifold that sported two or three two-barrel carburetors, as in stock car racing. Only in 1994, with the arrival of multipoint injection in the Omega, was this problem finally addressed.
  The performance of Opala 3.8 L was actually quite pleasing; with a top speed of 112.5 mph (181.1 km/h) and acceleration from 0 to 60 mph (97 km/h) in about 11 seconds, it was the fastest Brazilian car of its time, losing the title the following year to the Dodge Dart whose 318ci V8 had more power and torque. The 2.5 L fours did not offer as much vigor, but had enough torque enough for everyday use. The main complaint with the four-cylinder engines was their roughness—so rough that GM employees of the time called the engine "little Toyota", in allusion to the diesel engine installed in the locally built Toyota Bandeirante.
  Both the Especial and Luxo had a manual gearbox, rear wheel drive, front independent suspension and rear live axle, both with coil springs. In front, the suspension components were anchored to one side, set in the unibody with screws, later known as the subframe. The tires were the first tubeless tires used on a car manufactured in Brazil. It had a diaphragmatic (or "Chinese hat") clutch spring, which was becoming popular throughout the world. The Opala SS, originally only available with the "250" engine, was the first version to receive a four-speed manual gearbox. This was coupled with a tachomete
caption: Opala 250-S racing engine
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