On a new stock spark plug, my lawn mower would run out of gas with about 10% of the lawn left. After switching to the E3 plug, I could do the lawn on one tank and the mower seemed just little bit more able to power through the thicker parts of the lawn without dying.It gets four stars for two reasons:1. It's expensive.2. It seems to wear a little faster than a conventional plug.Despite its drawbacks, I use this plug exclusively in my small engines.