I had a 2003 S/C and put a cool air intake system in it, flowmaster exhaust system and upgraded the plugs, had the timing set and ran 91-93 octane. Never once did I get over 14 miles per gallon. I traded up to a 2007 and get 17-20 miles per gallon. This is my third Xterra and by far the best yet. Just have to start all over again adding mods to it. Don't count on getting any better MPG by adding a K&N filter. Heavy vehicle=shitty gas mileage.