on mine i have full exhaust, from the manifolds back, with a deep rumble, which is going to make my car run really rich......
and i fill up and drive on a full tank for 3 or 4 days, and i actually live outside of tampa bay, and have to drive in everyday for work...
i get probably about 22-28 miles to the gallon, and im also not very easy on my car (even with the milage, these 4.0 v8's they put in lexus' are very stout motors) i hotrod mine around everywhere i go ....
so take 'er easy and im positive you'll get better gas milage!