K-Car. After initial break in my 421B was running about 305 at the end of the 5 minute qualifiers. Ive got about a gallon through it now and last weekend it was temping at 265 at the end of 15 minute mains. Im using the #8 restrictor, mainly because it just plain works. I get about 7 minutes run time with it ans great power delivery. Im running the Nova Turbo #6 plugs in it and the AB 053 pipe. I will try the OS T-2050 on it this weekend to see if theres a difference. I also ran the o86 with waller on it as well. Had great results. But the AB 053 suited last weekends track perfectly.