So was dead certain about this mod before I bought my ap1. But now financial circumstances and realisation of running costs, I'm forced to consider mpg.
So the question is, will it be effected with this mod and if so, how much??

 

I doubt you will see any change at all. The only change would be if your driving style changes IE after the mod your foot gets heavier so you can hear the exhaust.

 

It's the same. 38mm here

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