There are so many variables when trying to achieve the magical 10 minutes to a tank in buggy. I know because I try to achieve the same thing. But the motors that are pretty well known to be able and get better than average runtime with any driver and under most conditions are the os v-spec or speed, novarossi plus 4, grp tuned .21, rb c6, and the mugen jx.21. I am sure there are more but these seem to be the most common when it comes to good fuel mileage.