ok I have heard of people putting trailing plug in the leading when getting ign upgrade. I this would have to be because the trailing has a bigger gap. Has anyone done this and did you feel the difference.

 

the heat ranges of the stock leading and trailing plugs are different... the trailing plugs are a "colder" heat range than the leadings. putting the colder heat range plugs in the leading position is better for high power applications, since the hotter plugs can overheat. (i found THAT out the hard way - melted out the ground electrodes on stock heat range plugs )