One very key factor that nobody has mentioned is the car. Having a light car and an efficient drive train helps with run time. Lightened axles, drive cups, as well as ceramic bearings, anything you can do to minimize the effort that the engine uses to get the car up to speed. The same driver on the same track, same motor, fuel, etc..but driving a different car, or a more efficient car of the same brand will get more mileage right away. IMO one of the most important things, and it doesn't even come from the engine, fuel or tune.

As far as the engine is concerned. You will get better mileage running the bottom lean and the top rich, considering the track isn't very high speed where there are wide open stretches everywhere. An engine that seems lean because it screams down the straight but blows lots of smoke out of every corner will not get very good mileage, but run cooler. An engine that is very crisp and peppy out of corners but runs a little rich down the straights will run a little warmer but get better mileage. Most guys I have seen that get great run time spend lots of time tuning the LSN to a specific point, usually to where it doesn't lean bog, but it's just 1-2 hours away from lean bogging, then by running the top a little rich you still get enough lubrication.