In 72 the factories were forced to use a new ratings system that entailed having all accessories installed on the engine and if I remember right they even had to have the trans bolted up and the rating was taken after the trans. For that reason every engine no matter what brand appeared to lose anywhere up to 75 hp but in reality they lost only a fraction of that amount due to lower compression and sometimes a milder cam. I'm not knocking 273's but they did not produce as much torque as a 318 and even if they did the 318 isn't a torque monster by any stretch of the imagination and the cam he's using is pretty fair size considering the engine's cubic inches.