I've never really calculated MPG, but I do reset my trip odometer each time I fill up and watch how many miles I can go on a full tank. My driving is mixed city and highway. When my VX was unmodified, I could go over 300-320 miles on a tank. After a few years and the addition of 33" tires, I was getting around 250. I recently installed the PV Muffler and hit 300 the other day. So that's about a 17% increase, or I'm guessing 4-5 MPG. I just bought a K&N Filter and will install it as soon as it arrives. I'll give an update in a couple of weeks!