I stepped down this year from a 21vzb non vspec to an 18tz in my buggy and I went from 7 1/2 mins to just over 10, and that's still running 30%, and letting it scream. I'm going to start playing lowering my epa settings, going to a slightly colder plug, and maybe, just maybe going down to 25% fuel. Not really looking for alot more time but if I could get consistant 12 min runs I'd be gravy. Just some ideas to play with.