The average mpg is, I think, a rolling 90-day average. As for the wheels, I put some Sport Edition E3's and a 1+ size tire on and saw a decent increase in coasting distance along with an increase in FE. I'm not too sure about the holes in the muffler though. Last year when I did the head work on my other Saturn, the rust exhaust pipe between the manifold and cat broke about 3/4 of the way in two and it just didn't seem to run real well until I had it repaired. Also, there could be a slight chance of CO getting into the cabin. Just some thoughts.
Horsepower is how hard you hit the wall, torque is how much of the wall you take with you.
Team Slow Burn