In 1973 and 1974, a special version of the 455, called the SD-455, was offered. The SD-455 utilized leftover components from Pontiac's 366 NASCAR engine, and was built as a full-bore racing engine that produced over 540 hp; the engine was subsequently "toned down" to appease the EPA and to meet GM's own strict power policy, which at the time required that no GM vehicle exceed 300 hp. As a result, the PMD engineers listed the SD-455 at 290 hp, but in reality it was producing, in final form, 371 hp SAE NET (or approximately 440 gross horsepower). What made this engine even more appealing was the ease with which it could be returned to its 500+ horsepower form.