[Manic]

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So it seems that you have a header-back exhaust along with a tune... well yes, you're going to get worse mileage. Better flow means your engine can breathe better... however breathing better also means breathing more. This means your engine will be using a bit more fuel, just the nature of the beast.

Add to that, your tune may eliminate the torque dip, but it serves a purpose and isn't just a random quirk with the car. The range where the torque dip is most commonly found is between 3k to 4.5k, highway cruising RPMs. Essentially, the torque dip helps with the car's MPG while cruising which ultimately helps with emissions. By flattening out the torque curve, you're sacrificing your MPG.