[STE92VE]

I have been doing research on this since I got my VIN and found out my 328i was being built with the N51 engine. This is what I know so far.

This is from BMW introduction of 2007 engines:
N51 Overview
In order to comply with SULEV requirements, the N51 is another variant of the N52
engine. There are various measures to meet the EPA/CARB standards, some of which
are familiar from the previous SULEV (M56) 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

There are 5 states that adhere to CARB SULEV engine requirements. CA, NY, ME, VT & MA. The N51 is being used in both auto and manual trannies.
It is basically the same engine as the N52 with slight modifications that reduce the CO2 emissions. As far as performance, I'm told there is no perceptable difference to the N52 other than that it adds about 30 lbs. to the car.
I'm waiting for my car to get on a ship in Bremerhaven and I will gladly post my impressions after I take delivery. If anyone else has the N51 and is currently driving it, maybe you could post your impressions as well.