The SD-455 was described as Pontiac's last stand and the last real muscle car. The SD-455 debuted quietly in 1973 as an option on the Formula and Trans Am versions of the Firebird. Its reported, likely made-up 310-hp rating easily embarrassed the 245-hp output of that year's top Camaro and put the SD in league with the big-block dinosaurs that had ruled only a few years before. Cleverly, Pontiac's team designed the engine to be an emissions-friendly starter kit. Purposely packaging a mild camshaft and relatively restrictive exhaust manifolds with a heavily fortified block. It even had provisions for a dry-sump oil pump. Forged steel connecting rods, forged aluminum pistons, and modified cylinder heads rounded out an engine that begged for extensive modifications and massive horsepower.

The 455 cu in 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 mains 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. Make no bones about it, a good nodular iron crank can easily live long and strong at 8000 rpm.

The 480737 code cam was originally specified for the SD455 engine and was fitted into the pre-production test cars, 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 second / 98 MPH range – results that are consistent with a 3,850 pound car and the rated 290 SAE net horsepower figure.

The SD-455 was a race bred engine that featured a special heavy duty block, forged pistons, four bolt main caps, a provision for dry sump oiling, round port heads that are known as the best flowing production Pontiac heads, header style exhaust manifolds and an 800 cfm carb. Extracting serious horsepower from this engine is as simple as a cam and ignition change.

Original SD-455 cars are valuable collectibles today.

Production figures for 73 are:

252 Trans Ams-180 automatics and 72 4-speed
43 Formula Firebirds-33 automatics and 10 4-speeds.

Figures for 74 are:

943 Trans Ams-731 automatics and 212 4-speed
58 Formula Firebirds.

During the motors 2 year production run Pontiac only made 1296 Super Duty 455's.

Specs: 1973 Trans-Am SD 455


Type: V-8, water-cooled, cast iron block and heads, 7 main bearings
Bore x Stroke: 4.15 x 4.21 in
Displacement: 455 cu in
Compression: 8.4:1
Carburetion: 1x4-bbl Rochester Quadrajet 800cfm
Power: 310 bhp @ 4000 rpm
Torque: 390 lbs-ft @ 3600 rpm
Curb Weight: 3854 lbs
Standing 1/4-mile: 13.54 sec @ 104.29mph
Top Speed: 165 mph

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