It's an interesting argument actually, take the ford 2.5 turbo diesel for example. Standard 93Kw and 329nm, after flowing the entire intake side it went up to 104Kw and 361nm. After doing all that we changed the boost pipes to 72mm, fitted a larger intercooler, upped the boost to 1.0 bar from the standard 0.8 and fitted a 63 mm exhaust. It went to 132Kw and 445 nm on the wheels. There are gains when polishing and porting any engine, the gains just differ.