Originally Posted by 240M3SRT
What gap are you running? I had the colder #7 ngk plugs at a stock .039 with 12.5 afr's. I went back and lowerd them all to .025 which is a huge decrease(what MD SRT6 is running 11.2's in the 1/4 on with nitrous and 181 pully and nitrous). I ran the car again and the freaking a/f went up to 13-13.4, wtf!
You're probably getting incomplete combustion due to the smaller gap/colder plug, or your car is going into enrichment from IAT/H2O temps.
Datalogging will tell which it is.