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Of all the variants of factory-built E46 BMW 3 Series, there’s a truly curious one that stands out as a touch strange. The E46 had a few models throughout the 1999-2006 production run: the 323i, 325i, 328i, 330i, and of course the mighty M3. But one that’s often forgotten is the 2003-2006 325i SULEV, which was only sold in four states and ostensibly designed to be environmentally friendly. 

SULEV is an acronym for Super Ultra Low Emissions Vehicle, which is a U.S. federal government classification for emissions standards. It starts with a Low Emission Vehicle (LEV), moves onto an Ultra Low Emission Vehicle (ULEV), then SULEV, and finally Partial Zero Emission Vehicle (PZEV). Cars are classified based on a percentage reduction of emissions compared to the average vehicle in the country. 

SULEV means that the car produces 90 percent fewer emissions than the average gas-powered car. PZEV means that cars produce zero evaporative emissions, like the fuel vapors that escape when you open your gas cap. States like California, New York, Massachusetts and Vermont require manufacturers to meet stricter emissions standards than the federal ones, but that’s not the entire story.

BMW went through the trouble of taking the normal 325i with the M54 engine and subjected it to a comprehensive host of engine modifications to make it qualify for SULEV. Before we approach the why of the effort, the what is shockingly comprehensive and advanced. The standard 2.5-liter M54 engine became the M56 through serious changes to the fuel system, crankcase ventilation system, cooling system, intake and exhaust.

Technical information from BMW about the 325i SULEV.
BMW

According to this BMW document, the car featured seven major changes. The most curious one to me is the addition of a “Direct Ozone Reduction System” radiator. It’s coated in a catalyst that reduces the ozone in the air traveling through the radiator, which I didn’t even know existed. 

BMW’s engineers added a hydrocarbon trap in the airbox as a supplement to the normal air filter so emissions can’t come back out of the engine, as well a throttle body that is described as “closed.” Normally, they are slightly open to allow idle air to leak through, but to meet PZEV they had to seal it.

They changed the pistons to have a different ringland, which changes how the piston rings seal the combustion chamber, and changed the fuel injectors for a finer spray pattern. Speaking of the fuel system, they changed the fuel tank and filler neck to stainless steel and sealed the failure-prone E46 fuel pump into the tank. As a result, it costs $1,000 to replace used, a cost for most owners of these cars don’t care to commit to. 

Different catalytic converters and VANOS tuning (BMW’s variable timing system) finish off the more mundane changes of the 325i SULEV. Not that the next change is exciting in any way, unless you own an E46 of your own and are seeking an upgrade on the notoriously terrible CCV system and plastic valve cover of the M54. The M56 on the 325i SULEV came with an aluminum valve cover with a more robust integrated CCV.

An aluminum M56 valve cover next to a normal plastic M54 valve cover in the engine bay of a 2004 BMW 330i.
Chris Rosales

I actually got one and installed it on my 330i ZHP to delete my CCV as a future failure point. The cool thing about this is that there are many junkyard M56 engines around. If you’re quick, you can swoop the valuable aluminum cover before anyone else gets there, but usually someone gets it and resells it for $150-$200. If you’re lucky, a yard will charge you $25 and you’ll have a solution for the plastic woes of an M54.

If you can’t be bothered to go dumpster diving and don’t mind paying a premium, the BMW part number for the aluminum valve cover is 11127521086, but it retails for over $800. You would be prudent to get a used one that is in good condition.

So, why did BMW go through all of this trouble to re-engineer a car for just four states? Beyond being compelled to by those regional regulations, BMW got valuable tax credits for making these low emissions cars. In 2002, California introduced legislation under AB 1493 that pushed new, stricter emissions standards in the state. Honestly, reading that document in the context of 2021 gave me sickening anxiety in my stomach, with the legislature foreseeing the devastating effects of climate change we’re seeing now, but I digress.

BMW did a lot of work to continue selling its other cars in the state and ended up making good parts that fit other cars in the process. I am a champion of OEM-plus sorts of upgrades, and this is as good as they come. Most everything else is an interesting response from a major automaker to ever strict emissions regulations, but the valve cover is a strange positive that enthusiasts ultimately benefit from. 

Now, the blueprint of the 325i SULEV is what modern cars have become, with cleaner-burning engines and an extreme focus on emissions performance. The technological marvel of modern internal combustion did not come from nowhere, and this weird old BMW started paving the way on a long, arduous road.

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