Yeah, my fuel mileage computer average mpg stays pretty close to my hand calc mpg (within .5 mpg, give or take). I have noticed that if you take your car outside of the norm of the last tank (i.e.-take a long highway trip when your last tank was all in town, etc.) that your average mpg readout will go way out of whack. I believed, during the one trip that I took, that a couple of tanks were around 5 mpg off.
As for the intake, I've seen and heard people on both sides of the mpg question. I don't know full details behind every situation, so I cannot verify in either direction. Speaking directly from the what I've seen on the graphs, I can see where the Typhoon could cause a loss in mileage. In non-RACECAR driving (below 3200 rpm), the Typhoon was showing roughly 5 hp less, with up to 8 ft lbs less tq.
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Hatch Nation #161