Interesting articles on the 273 engine

I had hardened valve seats installed in my current set, but I haven't run them yet. The valves were extremely recessed in these heads, making it mandatory. My car would get a lot of miles (if it ever gets back on the road).

There really isn't any option to run larger valves in the 273 because it's limited by the small bore size.

That 275HP motor mentioned was the "D-Dart" drag racing special. Very limited production. The street Commando was rated at 235HP.