I actually was wondering about that. I just looked at an NGK chart and a GR4 is equivalent to a 14 or 16 Champion heat range, so obviously a pretty hot plug. I got the plugs from Rock Auto when I did the cam and intake and ordered plugs for a 340 4 barrel. However, I just looked on their site again and noticed that they list the same plugs for a 318. I just assumed that the 340 plugs would be a little colder. I probably will try dropping one range and see how it does.
