Hks Spark Plugs...differences Between The Different Series.

[J-Boy]

Hi, anyone knows the differences between the different series of the HKS super fire racing plugs? What are the differences in the 5408-s40i(S-i series, ISO standard size), 50003-s40iL(S-iL series, long reach), 5408-s40g(S-G series), 5408-s40x(S-X series), 5408-r40(race pro), 5408-r40i(race pro). All of these are heat range 8. I'm currently using s40i and it works ok, just wondering if i could upgrade to like the 5408-r40i and it would still work as per normal. Car is a GTR32. Any advice would be great.

[J-Boy]

I've found that the RE series seems to be the sunken head series with the firing head inside instead of being outside normally, just like the NGK race competition plugs, the race-pro series seems to have a much smaller gap compared to the rest, but i cant tell the differences between the rest of the series yet.