is there any difference between a pontiac 455 sd and a 455?
http://en.wikipedia.org/wiki/Pontiac_V8_engine -- check out the 455 portion of this link it should give you some insite into the differences.
In 1973, a further refined and even stronger version, the Super Duty (SD) engine was introduced with "only" 310 hp (231 kW)/231 kW (SAE Net) using a similar camshaft specifications to the Ram Air IV 400. The 455 SD used round-port cylinder-heads similar to those used on the 1971 and 1972 455 HO, with specific "LS2" intake and cast-iron exhaust header-manifolds. Still, it was the strongest American engine offered that year. Its power was achieved through bending of EPA emissions-testing procedures, which led engineers to de-tune the engine to 290 hp (220 kW) via a camshaft change to the same profile used in the early RA III 400 engines for mid-1973 and 1974, after which point it was discontinued. While an evolution of the RA IV and H.O. engine designs, the 455 SD was a much improved engine. In addition to the more refined cylinder heads, block casting reinforcements in the lifter galley and main bearing oil pan rail area along with the addition of forged connecting rods with larger 7⁄16-inch-diameter (11 mm) bolts, the SD was made with a provision for dry sump oiling from the factory. This truly was a racing engine, detuned for use in passenger cars.
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