Thanks to Wikipedia...
[ QUOTE ]
In 1973 and 1974, a special version of the 455, called the SD-455, was offered.
The
SD-455 used the left over components from Pontiac's 366 NASCAR engine and was built as a full bore racing engine producing over 540 horsepower and
was then toned down to appease the EPA and to meet GM's strict horsepower policy which required all GM vehicles to hold the HP to under 300. As a result, the PMD engineers listed the SD-455 at
290 HP but in reality, was producing in final form,
371 HP SAE NET (Approx 440 gross horsepower).
What made this engine unique was the ease with which it could be returned to its 500+ horsepower form. The SD-455 is often considered the last of the true musclecar motors and by many, considered to be the most powerful factory Pontiac engine ever produced.
[/ QUOTE ]
All this with an 8.4:1 compression ratio...
