I'm a bit confused.. backpressure is a myth or not? I'm a rookie in this matter but I on your side 66sprint6
I've seen turboed car with 1m pipe instead exhaust line and I don't think it was "constructor" mistake. I'm thinking about exhaust pulses - waves.. It coud be similar or the same to the tricks in audio transmission lines. If I'm right, briefly there is a need to avoid stationary waves. Once I'll have consistent data about my mpg I'd like to make practical test - put simple cone cup (with let say 10mm hole) on the exhaust pipe. Then change hole diameter and again make a test.