Ways to improve a mustang?
With the exception of the syn lube, nothing you have done to your car will improve your average gas mileage. Freeing up the "flow" in your intake and exhaust may give you an increase in power, you may not be able to notice a difference. Everything you have done,so far
actually may decrease your mileage. Example...ram air hood will increase the drag on your 'stang at highway speeds..More drag will require you to go deeper into the throttle to maintain the same speed.
Experts recommend a computer tuner. The better ones have an economy tune as part of their offering. Also recommended are changes in your driving habits, keep your foot out of the throttle.(this is free)
I would be amazed at any car realizing a 17% increase in fuel mileage over stock.Modern computer controlled engines have been thoroughly engineered to provide an acceptable trade-off(balance) between power output , and fuel mileage.
I wonder?... If your MAIN concern in purchasing a car was fuel mileage, why did you choose a PERFORMANCE car?