In general, the problem is that the midpipe in 320i is 60,2mm and in 328i it is 75mm. You can check
RealOEM for details.
This is the reason BMW has not made it available for the 320i. Therefore also all the aftermarket exhausts will need modifing or an adapter but they should be OK otherwise to install.
The 328i OEM exhaust will not fit directly due to above reason.
I am getting mine tomorrow and will have it fitted probably next week so I can tell more (have been waiting for 6 weeks to get the 328i exhaust delivered).
Also, you will need the 328i rear diffuser to be fitter for the twin tail pipes. This is a direct fit for the M Sport model. Part number 51128054198.
Remus has a few
options. You will need an
adapter from them (Remus K7 adapter). Remus seem to be the only one who has made it available for the 320i.
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2013 BMW F30
320i - M-Sport, Alpine White, M Sport suspension and brakes, Sport AT, VSS, PDC, Xenon, High-beam assistant, Harman/Kardon, Extended BT, Rims 403M (summer 19") and 397 (winter 18"), M Performance: Exhaust, Rear Bumper Diffuser, Carbon fiber mirror caps, Carbon fiber rear spoiler, Black kidney grilles, Floor mats. 3M Brushed Black Metallic vinyl wrap roof.