Originally Posted by jcastle
There was some extensive discussion about it in this thread
Basically the 320i can't be brought up to the same figures as the 328i that easily as there are quite a few differences, i.e. compression ratio (11 vs. 10), different pistons, different backpipe (60,2mm vs. 75mm), software and maybe some other things people are not sure.
Normally tuning companies quote about 220-230 horsepowers and ~325Nm what can be achieved with the 320i (with external units).
Cut n paste from forum:
BMW has just announced a new entry level F30 3 series, the 320i. The 320i shares the same N20; TwinPower single turbo, twin scroll, 2.0 liter inline 4 cylinder engine as the 328i. The 320i is factory rated at 180 hp at 5,000 RPMs and 200 lb-ft of torque from 1,250 RPMs. Stacked next to the 328i with 240hp at 5000 RPMs and 255 lb-ft of torque from 1250 RPMs and the obvious question is what is the difference in the two engines.
The first obvious answer is there is something in BMW's DME control software that limits the power, most likely by limiting boost pressure, on the 320i. That appears to be true as both the 320 and the 328 use the same DME hardware (PN - 12148604210) and the same engine control system MEVD 17.2.9. With a software tweak the likely difference between the 320i and the 328i we go in search of other changes that might limit the 320is ability to make the same power the 328i N20 puts down.
The next easy target is the intake, exhaust manifold and turbo. Surprisingly they turned out to be the same part number. In fact the 320i and the 328i share the exact same part numbers for a majority of the engine components.
Shared engine components between F30 320i and 328i
Cylinder head - PN 11127624778
Connecting rods - PN 11247624616
Crankshaft - PN 11212212762
Intake manifold - PN 11617588126
Air box - PN 13717597589
Air filter - PN 13718507320
Intercooler - PN 17517618809
Radiator - PN 17117600520
Throttle body - PN 13547588625
HPFP - PN 13517584461
MAF - PN 13627602038
DME/ECU - PN 12148604210
Exhaust manifold/turbo - PN 11657642469