My racing partner, Chuck Erdman and I were running a 25SS in my test tank one Saturday afternoon many years ago. Our goal was to test a varity of spark plugs for performance differences. We tested a bunch of plugs, and in a final test, we installed my ignition test plugs. They were Champion L4J with the ground electrode removed in the lathe. Holy Cow, the engine ran faster than any other plug allowed. We duplicated out tests several times, with several different test wheels, and always a consistant water level in the tank. Thereafter, every 25SS powerhead I built for anyone was equipped with the modified L4Js. Ironically, many of the racers I built the engines for thought that I mistakenly left in a set of test plug, and never tried the engines As I provided. Their loss I guess, as we had discovered a proveable performance improvement. The Mercury ignition system was more than up for the challenge of the extreme spark gap, and we never had an ignition issue during all of the years that we ran the 25SS engines. On a side note, the 25XS engines did not respond to the large gap plugs in any style or brand. R.T.