Originally Posted by flinchy
the difference between being .25" over is still better for power than being .25" under.
the biggest issue is back pressure, you ideally want none, no leftover gases in the cylinder chamber.
regardless of the turbo being able to push in tons of air, it doesn't PUSH out burnt exhaust gases (being the exhaust valve is open when the intake is closed, mostly)
"2.75 or even 3" full catback would show absolutely immense gains"
Your talking up to 1/2" increase and you're talking about immense gains. It aint gonna happen.
BMW is certainly adept at fine balancing its N/A engines. The are damn near close to optimum balance of intake and exhaust to get the most power out of its engines. Going larger in tubing size isnt going to help, it will hinder low end tq certainly and likely hp. IMO.
OK. Let us know how it works out for ya. Dont forget the before after dynos.