a strong .21 will yield better lap times then a .28, not to mention the fuel economy you give up with a .28, all the newer truggies are geared for .21's. you just need a .21 with good bottom end power like the ebm5, ninja jx, v-spec those motors will give you as much power as the truck will handle and give you really good economy, tuned right you can get around 10 min run times with them