318 variances

Major difference between 1971 and 1972 was change from "SAE Gross" to "SAE Net" HP ratings. SAE Net was to reflect an "as installed" engine meaning an air cleaner, fan belt, full exhaust system etc... This was in response to some of the absolute bullsh*t ratings in the 60's, driven by the insurance industry. A level playing field if you will.

Compression ratios and timing advance curves also took a dive, but that really didn't make much difference on the 318 or 225. The hard parts really didn't change much. A 1968-71 318 probably made 150 "Net HP" on a good day.