Compression Question

The horsepower didn't decline in 72, they way they measured it did. Prior to 72 the horsepower was gross HP, that is, it was measured at the crank without accessories (i.e., no water pump, alternator, AC compressor, power steering pump, air filter or exhaust system). In 72 the manufacturers were required to report NET HP which included all those items on the engine just as it would be in the engine compartment.

73 was the first year of emission standards that resulted in compression ratio's being lowered to meet them.