Originally Posted by jblaine
FWIW, I tuned the GT100 map to 11.6:1 and 20.8psi from 3800-6000 yesterday and tonight with nothing outside my new knock threshold curve. EGTs were 1600F at 6800RPM. Ran fine, sounded fine.
I have a few customers that have issues running colder plugs on the STI engine so they appear to be more sensitive than your combination due to the lower compression. You know if it gives you piece of mind and you're not experiencing cold start or cold running issue then go with it.
I still use heat range 6 plugs on my car and have done so approaching 700 whp. With a drag turbo I make around 600 whp and have sprayed a 70 shot of N20 on top of that. So far I have not felt the need to go with a colder plug on the STI application for normal street use or drag racing.
Once I get the Time Attack car back from California I'll check the insulators for any over heating since the car was used for extended periods at high rpm and very high egts. For road racing a colder plug may be beneficial if there are signs of over heating the insulator.