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Chevrolet Opala 1969-1992
The Chevrolet Opala was a mid-size car sold by General Motors do Brasil from 1969 to 1992. It was derived from the German Opel Rekord and Commodore, but used GM USA sourced engines, two four-cylinder engines: the Chevrolet 153 4-cylinder from Chevy II/Nova which later got a new crankshaft and cylinders changing its size to 151 (usually mistaken as 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 variation, the Opala Caravan. It was replaced by the Chevrolet Omega in 1992, also an Opel spinoff. Before this car, Chevrolet only built light trucks and pick-up trucks, so, the Opala was its first passenger car made by GM in Brazil.
It was used by the Brazilian Police for many years. The military dictatorship used the Opala for its agents through the 1970s. Its reliability and easy maintenance made the Opala the choice of many taxi drivers and also popular on racetracks.
Its 250 cubic inch engine (4.1 L) was used in its replacement, the Chevrolet Omega, but making use of Electronic Fuel Injection, in GLS and CD trims from 1995 to 1998. Some of the components and chassis were used for some exotic cars as Santa Matilde, Puma GTB and some replicas as the Fera XK (Jaguar XK).
At the opening of the sixth São Paulo Auto Show, on November 23, 1968, the Opala appeared on a rotating stage in a 16,140 square feet (1,499 m2) stand. Around the novelty there were several spectacles including the presence of Stirling Moss and several Opala models were shown every half hour.
The first model was the four-door sedan in the trims "Especial" (Special) and "Luxo" (Deluxe). Its attractive lines used the solution of curvy lines from the windscreen to rear fender, a shape that was referred to as "Coke Bottle style", already in use at the time, as it was first shown on 1967 Chevrolet Camaro, 1967 Pontiac Firebird and 1968 Chevrolet Corvette, but some hints of the upcoming style were already clear on the 1965 Chevrolet Impala fastback coupé. A hardtop coupe was also offered with a silhouette resembling the first-generation Camaro/Firebird. The round headlamps (not squared, as in the Opel Rekord and Commodore), distinguished an egg-crate grille, distinctively Chevrolet style (based on the U.S. 1968 Chevy II Nova), that separated the Opala from its European Opel siblings and the park/turning lamps were fitted below in the front bumper. In the back, a chrome strip with the "Chevrolet" name in black linked in the more expensive trim, the small rectangular taillights (similar to the U.S. 1967 Chevrolet Chevelle), in the extremities of the rear overhang, with the small reverse lights in the rear-bumper. Just above this was the fuel tank cap. The "Opala" badge (similar to the U.S. Chevrolet Impala font style), was fitted in the rear fenders, and the engine badges - 2500 or 3800 - next to the front doors. The chrome wheelcovers fitted just fine with the whitewall tires.
Both versions came standard with front bench seats (bucket seats weren't available at the beginning of production, but were later adopted) and steering-column shifter. The two models differed in trim levels: reverse lights, fuel tank lock and rear valance chrome strip were available only on "Luxo" model.
[B]Development[/B]
In the fall of 1970 a more luxurious version was added, it received the name Comodoro, reflecting Europe's Opel Commodore. In some years the Comodoro-4 received a somewhat more powerful version of the 2.5 liter four, with 88 PS (65 kW) rather than 80 PS (59 kW). The same engine was used for the Opala SS-4. Even more luxurious was the Diplomata, which appeared in November 1979.
[B]Engines[/B]
Under the hood, which opened backwards, the Opala originally offered two engine choices: the straight-four 153 cu in (2,507 cc) and the straight-six 230 cu in (3,764 cc). They were of a very traditional design, with cast iron cylinder block and head, overhead valves, pushrods and steel pressed rocker arms, whose spherical fulcrum was a proprietary GM's creation - fuel was fed from either single or double barrel carburetors. In 1971 the 3.8 had been replaced by the bigger 4.1 (4,093 cc or 250 cu in).
The larger engine crankshaft bearings had seven supports (five in four-cylinders) and the generous, if not even redundant, size of its inner moving parts helped with its durability and exceptional smoothness. The hydraulic valve lifters contributed to that later feature, easying maintenance.
The straight-six biggest limitation through the years was poor distribution of air-fuel ratio to the cylinders. Number one and six received the poorest, with higher percentage of air in the mixture, while the central ones tended to get richer mixture, unbalancing the stoichiometric engine efficiency. That bad feature was easily 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 Omega and the multipoint injection, the problem was finally solved.
The performance of Opala 3.8 L was actually very pleasing: with a top speed of 112.5 mph (181.1 km/h) and acceleration time from 0 to 60 mph (97 km/h) in about 11 seconds, was the fastest Brazilian car of its time, while it was losing the post after a year to the Dodge Dart whose 318 cu in V8 had all a straight-six was missing. The two 2.5 L fours did not offer so much brio, but were torquey enough for everyday use. The main complain over the four-cylinder engines was about their roughness - so rough that at the time GM employees called the Four "little Toyota", in allusion to the diesel engine installed in the locally made Toyota Bandeirante (Brazil's name for the Land Cruiser).
Both versions, Especial and Luxo, had the three-speed manual gearbox, rear wheel drive, front independent suspension and rear live axle, both with helical springs. In front, the suspension elements were anchored to one side, set in unibody by screws, which only later would be known as subframe. The tires were the first tubeless to be used in a model manufactured in Brazil, and used clutch spring type "Chinese hat", or diaphragmatic spring, which began to popularize in the world. The sporting 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 rev counter and lots of matte black striping.
[B]The 250-S Engine[/B]
When the long-duration races restarted in Brazil, in 1973, the Opala found a great competitor, the Ford Maverick, which was powered by an engine whose displacement was almost one liter bigger. It took Bob Sharp and Jan Balder, that gained a second place in the "24 Hours of Interlagos", in August of that year in an Opala, to pressure GMB to field on race tracks a more powerful engine.
By coincidence, engine development manager, Roberto B. Beccardi, was working on this engine hopping-up project out of his own initiative, but he did lack impulse from factory and was not obtaining any approval. This impulse came right from these two pilots.
Thus, in July 1974 GM started to offer the 250-S engine as an option for the Opala 4100. It was slightly different from the version that would be launched two years later: the project of the motor was similar to that of the four-cylinder units, did not get a vibration damper and the cooling fan came from the standard 2500, with four blades instead of six.
The Opala was now much faster than the Maverick GT, and Ford did not waste time. It quickly homologated a version with four-barrel carburetor, simply called "Quadrijet" in Brazilian parlance, and have no relationship with GM own Rochester Quadrajet carburetor, found on GM Corp. various V8 engines. In the racetracks, the accounting determinative factor for winning was pilots' skill and pit organization on the track. The rivals walked side by side.
[SIZE="1"]Source: wikipedia.org[/SIZE]
