When mine was stock, after a complete tune up, and adding a piece in the intake called a Tornado, and a K&N, the best I got a highway trip was 19.2. Now, with ported heads, 3" magnaflow exhaust, 24 lb injectors, and few more things, my check yielded 13.6 mpg. I normally average around 14 though.
wish I got near that with my R/T, I only average around 11 mpg, only engine mod is a K&N filter charger intake.
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360 Intakez CAI / Magnaflow catback exhaust / Black headlights / LED tailights
Remove side molding / Custom stereo with indash computer / custom painted interior trim