I think fuel economy should not be a consideration when running a Cossie, It is a performance car and as such its going to burn fuel. How much fuel you use depends a lot on the condition and the spec of your car and also how you drive it. Even in standard tune they where never really economical with around 22 - 25 mpg.

Power requires fuel which in turn costs money, thats the deal!!

CheeRS, Mike.