Pontiac Firebird Trans AM 2. Generation 455 Super Duty 1973
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Car producer : |
Pontiac |
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Model: |
Firebird Trans AM 2. Generation 455 Super Duty 1973 |
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Year: |
1970-1981 |
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Type: |
Coupe |
The second generation debut for the 1970 model year was delayed until February 26, 1970, because of tooling and engineering problems; thus, its popular designation as a 1970½ model, while leftover 1969s were listed in early Pontiac literature without a model-year identification.
There were two Ram Air 400 cu in (6.6 L) engines for 1970: the 335 hp (250 kW) Ram Air III (366 hp (273 kW) in GTO) and the 345 hp (257 kW) Ram Air IV (370 hp (280 kW) in GTO) that were carried over from 1969. The difference between the GTO and Firebird engines was the secondary carburetor linkage which prevented the rear barrels from opening completely. Bending the linkage to allow full carburetor operation resulted in identical engine performance.
Curb weights rose dramatically in the 1974 model year due to the implementation of 5 mph (8.0 km/h) telescoping bumpers and various other crash and safety related structural enhancements; SD455 Trans Ams weighed in at 3,850 lb (1,750 kg) in their first year of production (1974 model year).
The 455 engine available in the second generation Firebird Trans Am was arguably the last high-performance engine of the original muscle car generation. The 455 cu in (7.5 L) engine made its first appearance in the Firebird in 1971 as the 455-HO, which continued through the 1972 model year. In 1973 and 1974, a special version of the 455, called the Super Duty 455 (SD-455), was offered. The SD-455 consisted of a strengthened cylinder block that included 4-bolt main bearings and added material in various locations for improved strength. Original plans called for a forged crankshaft, although actual production SD455s received nodular iron crankshafts with minor enhancements. Forged rods and forged aluminum pistons were specified, as were unique high-flow cylinder heads.
The 480737 code cam (identical grind to the RAIV "041" cam) was originally specified for the SD455 engine and was fitted into the "pre-production" test cars (source: former Pontiac Special Projects Engineer Skip McCully), one of which was tested by both HOT ROD and CAR AND DRIVER magazines. However, actual production cars were fitted with the milder 493323 cam and 1.5:1 rocker ratios, due to the ever-tightening emissions standards of the era. This cam and rocker combination, combined with a low compression ratio of 8.4:1 advertised (7.9:1 actual) yielded 290 SAE net horsepower. It should also be noted that production SD455 cars did not have functional hood scoops, while the "pre-production" test cars did.
Actual production cars yielded 1/4 mile results in the high 14 to 15.0 second/98 MPH range (sources: MOTOR TREND MAGAZINE, July '73 and Roger Huntington's book, AMERICAN SUPERCAR) – results that are consistent with a 3,850 pound car (plus driver) and the rated 290 SAE net horsepower figure. (An original rating of 310 SAE net horsepower had been assigned to the SD455, though that rating was based on the emissions non-compliant "pre-production" engines, as discussed above. That rating appeared in published 1973 model year Pontiac literature, which had been printed prior to the "pre-production" engines "barely passing" emissions testing, and the last minute switch to what became the production engine. 1974 model year production literature listed the specifications of the production engine (290 SAE net horsepower).
A production line stock SD455 produced 253 rear wheel HP on a chassis dyno, as reported by HIGH PERFORMANCE PONTIAC magazine (January, 2007). This is also consistent with the 290 SAE Net horsepower factory rating (as measured at the crankshaft). Skip McCully verified that no production SD455s released to the public were fitted with the 480737 cam. When asked about the compromises for the production SD455 engine, Mr. McCully responded, "Compression, camshaft, jetting, and vacuum advance." He followed by stating that he would have preferred a compression ratio of 10.25:1, a camshaft with 041 valve timing, slightly richer carburetor jetting, and as much vacuum advance as the engine would tolerate. (May, 2005 issue of HIGH PERFORMANCE PONTIAC Magazine). Regrettably, that proved to be impossible due to the emissions regulations of the era.
During a 1972 strike, the Firebird (and the sister F-body Camaro) were nearly dropped. Pontiac offered the 455 through the 1976 model year, but tightening restrictions on vehicle emissions guaranteed its demise. Thus, the 1976 Trans Am was the last of the "Big Cube Birds," with only 7,100 units produced with the 455 engine.
The Trans Am was a specialty package for the Firebird, typically upgrading handling, suspension, and horsepower, as well as minor appearance modifications such as exclusive hoods, spoilers, fog lights and wheels. In using the name Trans Am, a registered trademark, GM agreed to pay $5 per car sold to the SCCA. Four distinct generations were produced between 1969 and 2002. These cars were built on the F-body platform, which was also shared by the Chevrolet Camaro.
Despite its name, the Trans Am was not initially used in the Trans Am Series, as its smallest engine exceeded the SCCA's five liter displacement limit.
The second generation was available from 1970 to 1981.
