Pontiac Firebird, with rocket launchers, turbo boosters, 80 miles to the gallon (with a 10 cylinder engine, or a hybrid), capable of hitting mach 1 on a good day, and railguns!
What? You didn't say the car had to exist.
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Proud member of the Global Defence Force.
http://gifninja.com/animatedgifs/120003/phoenixtrio.gif