A possibly simple or not so simple question.
 

Just lookin looking round at scooby bits etc and they all do so many lb/ft etc. For example a new downpipe may increase torque etc (as I understand it) but does it increase or decrease fuel consumption. You read about good mods, ie downpipe, de catted exhaust etc but do they increase or decrease fuel consumption ? Ie your making the air flow/exhaust flow more efficient or is that not the case?

I found with a full decat, I get slightly better fuel ecomony

Well, that was until I did some other mods too LOL