Factory HP ratings -BS or what happened?

Prior to 1971-72 (?) horsepower ratings were sort of a free-for-all. If I was running an engine for power ratings, I wouldn't have to run any engine accessories and could run a tuned header if I wanted. Air filter, smog equipment; nope could ditch that too. I could also tune the engine for peak power while the engine was running. This means I could retard the dizzy to start, then advance it to optimum at higher rpm. Not only that, I could jet the carburetor for maximum power.

The SAE standard that had to be adopted in 71 or 72 cut a lot of that non-sense out. Engines were required to run with accessories the model car came equipped with. They also had to run a full exhaust system. Remember that by 1975 just about everything was trying to exhale through a catalyst. The result was plummeting horsepower and confused people wondering where it went. The short answer is some of it went to smog abatement the rest went to method of measurement change.