They are just different. Hard to explain, without changing everything the 318 will not pull and rev as high as the 273, which for me is the draw for the 273. You can get a 318 to run, but for me, you pretty much make it into a 340 - 22 cu in. It takes a lot more than a cam change, and then you still have a cast crank. A 273 takes a solid cam and valve spring change, a 4 barrel intake and a carb. High Performance Done.
