Q: i was told that when a v8 engine is put into a coupe, its just like a v6 cuz it weighs less and dosent waste that much gas when compared, just wanted to know if this is true on all coupes
A: I'm not sure about the A5 but if its two well engineered engines and you compared them side by side with the same moderate acceleration you would get the same mileage. If its the same car, itll be the same weight and drag (a little more weight for the V8 engine itself, but on an Audi itll probably be aluminum) so it should require only the same energy to move the mass of the car. A good example of the vehicle mass making more of a difference than the engine size: BMW X5, on the older body style, the inline 6 gets worse mileage than the V8 because the inline six is working just as hard as the V8 to move the car, but its working on its upper limit so it strains and uses more fuel. Often a V8 engine option gives lower mileage because its less efficient than a smaller engine, but with Audi that certainly won't be an issue, German engineers strive for efficiency. I'd go V8 on the A5, if youre light on the throttle for your daily driving, the mileage won't be bad, it definitely wont be a difference of 4 miles per gallon, and then you'll have the option of melting your face back towards your ears when you really get on the throttle.