On the Interstate running 75 plus I am around 22 MPG with all of my mods. In town and because of the drone, I usually am running mostly 3rd gear and around 3000 RPMs so my MPG is way down... probably close to you. Maybe 8 - 10. But hey, that is the price we pay to play!!!

 

8 mpg is way off. With my mods I am getting 12-14 and all my driving is short distance city style with lots of thottle and brake.

 

If you had your car dyno run or retuned which you should have then you can expect really low mpg. I had cams installed a few days ago. Day after I got it back 8.6. Day later 10.8 and now today around 11mpg. And I'm no lighter on the gas then I was before. Expect a 1-2mpg loss at most. They do lower mpg because of how they affect the car. More gas is needed in lower rpm to keep it as smooth as a no cam mustang. It's well worth it though.