1972 454 Versus 1971 454

I have a 1972 LS5 (454). Can anyone tell me what, if any are the differences between the 1971 454 and the 1972 454. They both have 8.5/1 compression ratio, but are vastly different in their horsepower rating, 365/270. Any information would be greatly appreciated. Thanks, Jimmie

First thing is that in 72 they changed how hp was rated, 2nd there was a little more anti-smog equip't put on the 72 so if you compared apples to apples the gross hp would be just a little less in 72 from 71.