It is corrigated on the inside aswell.. I reckon there would be some drag but from going from the stock setup to this has made a world off difference and I'm happy how it currently performs, but yea I'd imagine there would be gains with a 'normal' pipe.. It's a pretty hardcore bit of pipe, pretty thick like the factory rubber hoses, and had metal ribs in each corrigation to keep it from flexing, so it's fairly strong.. There isn't anything aftermarket to suit what I'm trying to do, so for the meantime it'll have to do..