Pontiac Firebird Formula 400
Second Generation Pontiac Firebird (1970-81): 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 1974 models featured a redesigned "shovel-nose" front end and new wide "slotted" taillights. In 1974, Pontiac offered two base engines for the Firebird: a 100 hp (75 kW) 250 cu in (4.1 L) inline-6 and a 155 hp (116 kW) 350 cu in (5.7 L) V8. Available were 175 hp (130 kW) to 225 hp (168 kW) 400 cu in (6.6 L) V8 engines, as well as the 455 cu in (7.5 L) produced 215 hp (160 kW) or 250 hp (190 kW), while the SD-455 produced 290 hp (220 kW). The 400, 455, and SD-455 engines were offered in the Trans Am and Formula models during 1974
The 1975 models featured a new wraparound rear window with a revised roofline and the turn signals were moved up from the valance panel to the grills which distinguished it from the previous year model. The Super Duty engine, Muncie 4-speed, and TurboHydramatic were no longer available in 1975.
The 400 was standard in the Trans Am and the 455 was optional for both 1975 and 1976 models.
Source: Wikipedia, 2014