They work but because the 318 has a bigger bore you can put big valve heads on for more performance. A 318 with X or J heads and the right parts to go with can get you to 400 hp. without too many tricks. The 273 is a fun little engine but it lacks bore size and doesn't work well with large valves or large combustion chambers. A friend had a 318 from a Notchback Barracuda from the 70's. It had J heads, Crane Fireball cam, headers, and intake and carb. It screamed. He rebuilt it last year with 318 heads with 340 valves and the same combination. It screams too. tmm
