When the new F30 chassis BMW 328i was released in early 2012, all of them came with the 4 cylinder N20 engine. The N20 engine is rated as a Ultra Low Emissions Vehicle (ULEV).
However, starting around March 2012 build date, BMW started replacing the N20 engines with the N26 engine. The N26 engine is rated as a Super Ultra Low Emissions Vehicle (SULEV). There are 13 states that will have SULEV cars. They are California, Arizona, Conneticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington and the District of Columbia. Thus, 99% of the cars built after March 2012 in those states are N26 engines. While, the remaining states should have N20 engines, there still is a chance you may get the N26 engine. The same applies for the states that have the SULEV cars. The best way to tell is to check your own individual cars from the guide below.
Emissions sticker under the factory hood (bonnet):
The best way to tell if you have an N20 or N26 engine is to check the engine bay. Underneath the factory hood (bonnet), there will be a sticker showing the emissions specs of the car. The sticker will look like this:
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N20 Engine - ULEV EMISSIONS STICKER
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If you have an N20 engine, it will say ULEV. If it is an N26 engine, it will say SULEV.
Downpipe:
The N20 exhaust system uses standard slip fit joint and clamps to connect. The downpipe will look like below:
The N26 exhaust system uses a ball and flare joint and clamps to connect. The downpipe will look like below:
Intake:
The factory intake boxes between the N20 and N26 look almost identical. However, the difference is the N26 has an extra "nipple" for a vacuum port shown here:
