Saturday 16 March 2019
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 USA-sourced engines and a local design styling. Two four-cylinder engines: the Chevrolet 153ci 4-cylinder from Chevy II/Nova, which later got a new crankshaft stroke and cylinder bore, changing its size to 151ci (usually mistaken for the Pontiac Iron Duke engine), and the six-cylinder 250 from the contemporary line of North American car/light truck production. 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's long-lived 250-cubic-inch (4.1 L) engine was also used in its replacement, the Chevrolet Omega (which featured electronic fuel injection in the GLS and CD trims) from 1995 to 1998. Some of the Opalas components and chassis were used in other Brazilian cars such as the Santa Matilde, Puma GTB, and the Fera XK (a Jaguar XK replica). Leva pau de corsa 1.0.
Founded in January 1925, General Motors do Brasil originally only assembled, and later, manufactured, light trucks and utilities until the mid-1960s, when they decided to produce their first Brazilian-made passenger car.
The options varied between the traditional, large, more expensive American-style cars that GM was already selling in the United States line, such as the Impala, and the lighter and more economical models from German GM-subsidiary Opel (such as the Kadett, Olympia, Rekord and Commodore) which were already imported to Brazil in small quantities. After wavering between the small Kadett and the somewhat larger Rekord/Commodore line, GMB opted for the latter, but later introduced the Kadett as well.
On November 23, 1966, in a Press Conference at the Club Atlético Paulistano in São Paulo, GM publicly announced the existence of "Project 676", which would become the Chevrolet Opala.
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 (2,507 cc) straight-four and a 230 cu in (3,764 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. In 1973 the four cylinder was replaced by Pontiac's 151 cu in (2,474 cc) "Iron Duke" engine, of generally similar configuration The 3.8 had already been replaced by the bigger 4.1 (4,093 cc or 250 cu in) in 1971.
The engines used in the Opala had been already used for years in the USA: the 153ci had emerged in the 1962 Chevrolet Nova, becoming the first inline four in a Chevrolet since 1928, and the 230ci appeared in the 1963 Impala. The 151 cu in Pontiac Iron Duke was also found in AMC's Jeeps and Eagles, and was known for its versatility and toughness. Known for its reliability, the 153ci was an industry benchmark until the 1980s. The straight-six later served as a stationary engine, a school bus engine, and even found its way into forklifts.
The 6-cylinder engine crankshaft had seven main bearings (five in 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 the engine's problem finally solved.
The performance of Opala 3.8L 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 two 2.5L 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 tachometer and lots of matte black striping.
- engine: 4 cylinders
- capacity: 2500 cc
- horsepower: 98 HP
- gearbox: 5+1
- top speed: 160 km/h