Id hope the environment is considered in everyones quest for mpg.
Granted I plan on a new exhaust for my kick, I also plan on adding a high flow cat in place of the oem one. Gasoline engines I thinkwould be easy to add a cat to clean it up, not sure about the diesels. I hear the system collects the soot, then burn it off every so often in a regen cycle. I doubt something like that could be fitted to a diesel lawn mower engine.