14mpg on first tank of gas in stock car...

I think your issue is you're looking for MPG while its really SPG... For me I get endless smiles per gallon and even more when I push the go fast pedal.

i get about 16.3 in my widebody scatpack... its still in break in with around 800 miles on it.. I got around 19mpg in my cobra and it was a big Hp car (for its time) but the centrifugal SC helped a TON

Highway driving I get 20 mpg exactly, lay on her much less, maybe you need a better tune ?

It's just so much fun building boost in these cars. With that comes a price of lower fuel economy. As Alfred E. Neuman would say, "what, me worry?" Just keep enjoying your Cobra. Time for more fun? Take the step from intake/exhaust mods to a smaller upper and tune. And with a good, conservative tune will come slightly better fuel mileage overall.