I can't believe it either.
Yep, after switching over to the VX as the daily driver, I took down my start miles for my last fill-up. I have to keep track of miles for mileage reimbursement. To my surprise, my total mileage for the last tank was 365 miles. One caveat, I almost ran her dry. She stumbled about 1/2 mile from home when I turned around as I'd forgotten my wallet at home. Fate?
Anyway, I'd been driving a 2005 Mitsubishi Evolution VIII (turbocharged 4-cylinder, AWD, about 300hp/300torque at the wheels) with a few small modifications as my work vehicle. As gas prices rose sharply, I began to drive like I owned it and began to experiment with how to get the best mileage out of the vehicle. I'm reimbursed .30 cents a mile (pitiful) so it's worth my effort. While I had been short shifting prior to peak torque (and probably peak VE), I noticed my mileage was about the same as if I'd accelerated with positive boost (not pushing it hard, but decent acceleration). Essentially I was lugging the engine in many situations. So I began shifting at 4K rpm, 500 rpm above peak torque and I stayed well within the vacuum zone and out of positive boost pressure. Revving the engine a bit higher helped me stay out of the lower rev range and thus lugging the engine when I switched into a numerically higher gear. My mileage went way up. Where I'd been struggling to get 260 miles out of a tank, I was now easily at 300. Modifying my driving a bit more, I'd see over 310 to 320 in city driving on a regular basis.
In the VX, there's really no way to control shift points and vacuum pull (which determines how much fuel your injectors push) like you can in a manual transmission vehicle. So I skipped the "normal" transmission mode and I leave it in sport. This is mostly because even under light acceleration, it tends to use higher revs, lower gear and thus it puts less load on the engine. Pulling from low revs in a higher gear uses more fuel.
I also coast to stoplights/signs. I don't accelerate hard, but I don't hold up traffic. A/C is on all the time (it's Florida) and I drive with my lights on. I also try to find routes that don't have as many stop and go situations and usually, I avoid the highway and will take a slower road with no traffic lights to reach the same destination when possible. Also, I use cruise control whenever I'm able. Every time you accelerate, the injectors squirt a bit more fuel than needed acting like an "accelerator pump" on a carb. Keeping a steady throttle reduces overall fuel load over time.
I have put the stock intake back on where previously, I had an Injen on there. I did not take a mileage reading with the Injen on for a full tank of gas as I switched it out mid-tank for the stocker.
I have an Aero exhaust en route. I should be able to run through one more tank before I'm able to put it on just to verify. Will of course report back after I install the new muffler. I may end up replacing my catalytic converters depending on how good/poor they look. I thought for sure they'd be toast by now but I guess not.
Also, I recently had the transmission fluid changed along with the filter. Replaced the front and rear differentials and the TOD. I used Royal Purple in the diffs, normal weight, and Castrol synthetic in everything else. I have a 1999 so I have the 16" wheel package and I have the rear seats removed although any loss in weight has been regained with all the camera equipment I carry in the car. The car is over 120,000 miles now. I thought about switching to 18" rims but I may not do that now. I have stock-sized tires on there, Firestones, with 34psi of pressure all around.
So...I'm hoping to hit 375 WITHOUT running her dry after the exhaust changeout. We'll see..I know others have reported mileage loss switching mufflers out. There are lots of reasons why this occurs and there is good reason why, if the car is driven in the correct manner, freeing up back pressure on the exhaust side will work to improve mileage as well.
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