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Found this:
Low Emission Vehicle (LEV): This is the average vehicle, the minimum that you can legally drive in California.
Ultra Low Emission Vehicle (ULEV): ULEVs are described as 50% cleaner than the average new vehicle for the model year.
Super Ultra Low Emission Vehicle (SULEV): SULEVs are 90% cleaner than the average new vehicle for the model year.
The 328i SULEV uses the N51 versus the N52 engine. In order to comply with SULEV requirements, the N51 is a variant of the N52 engine. Some of the SULEV measures for the N51 include:
• Near engine catalyst with additional underbody catalyst
• Secondary air system
• Optimized combustion chamber geometry in cylinder head
• Modified piston crown for lower compression
• Plastic valve cover with integrated crankcase vent valve and separator (from N52KP)
• Stainless steel fuel lines with threaded connections
• Radiator with “Prem-air” coating
• Throttle system - EGAS08 carried over from N52KP
• Airbox with Activated carbon filter for EVAP control
• Purge system pipes are made from “optimized” plastic
BMW claims there is no performance difference other than the increase in weight which adds about 30 lbs.
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