Yeah, I was running 9s for a while to try to drop my EGTs. Didn't seem to make any difference. I didn't have any problems with fouling, but I took them out and went back to 7s because the car got slower by 0.3 secs in the 1/4 mile. This was not necessarily a result of using the colder plugs, but I reversed everything I changed between the faster and slower times. Next time I am at the dragstrip I will change each thing one at a time to hopefully find out what really caused it.
Certainly with NGK's, the higher the number the colder the plug.
Cold plugs are Ok for continuously driving hard (ie racing, hill climbing etc) but for road use you can't go wrong with the standard £6 per set NGK's. A few years back I tried all the 'special plugs' and did not notice any performance gains at all. The only time I have had a need to use a cold plug is with tuned two stroke engines (to stop piston crown melt down
Thanks for the info. Our GEMS friend from T and amp;T concurs that the stock plugs are suficient for streat/strip use. I received my new Daiken twin disk clutch and called Peter for break in directions last week. He has his six in the mid 10's but bent a rod. Apparently 500 HP is the practical limit for the stock rods. He is thinking of Titanium rods next.