Re: heat
No, Star.<br /><br />A given engine runs best with the heat range specified by the engineers who designed it, with one small "except".<br /><br />As an example, take a older JohnnyRude small twin from 3 to 6hp. For all around and high speed performance most of them call for Champion J4C plugs. A few will call for J6C.<br /><br />For mostly low speed and trolling they do a bit better with the hotter J6C. They are less likely to foul the plugs, but don't do as well at WOT, where the J4C works better.