Well I do not own a Cobra but I do own an 01 GT that is my driver. The 4.6 runs as strong at 80K miles as it did when I bought it new. The only modifications Ive made to it engine wise are a BBK cold air kit, underdrive pulleys and purchased a performace tuner off Ebay. I get 19-20 city and 22-28 hwy of course driving conditions and how heavy my foot is always affects the mileage.