Although BMW has made big changes to the 7-Series and 3-Series models, the 5-Series has not gotten the same sort of attention. Think of it as the middle child. What the company has done is to leverage some of its resources—particularly in powertrain—by deploying them in the latest versions of the 5-Series. The most prominent change is the replacement of the base 2.5-liter in-line 6-cylinder engine with the 3.0-liter N52 6-cylinder found in the 3-Series Coupe, resulting in the base 5-Series carrying the “528i” and “xi” (all-wheel drive) monikers. The engine produces 230 horsepower, a 15 horsepower increase from the outgoing 525i. The 530i and xi models are sent packing, replaced by the 535i and xi, both of which get the 3 coupe’s new N54 twin-turbo 6-cylinder engine producing 300 horsepower, a 10 horsepower increase over the 525 engine. What’s interesting to note about this is that this is the first turbocharged engine that BMW has offered in more than 30 years, so evidentially it is finding it to be of greater applicability. The top-range 550i, meanwhile, retains its 4.8-liter V-8, producing 360 horsepower.
BMW is particularly proud of the N52 engine because it marks several significant milestones for the automaker. Claiming it is the first full-production aluminum/magnesium composite engine ever offered, BMW says the materials help to reduce overall weight, enhancing overall vehicle weight distribution. The lower portion of the block is constructed from magnesium-aluminum alloy and devised from the V10 engine found in the M5 and M6, while the insert utilizes a silicon-impregnated aluminum alloy (Alusil), similar to the material used in BMW’s V8 and V12 engines. Added weight savings are derived from the use of hollow camshafts (cutting 2.6 lb. each) and the composite material used for the camshaft cover, along with the 2-mm thick exhaust headers’ flanges, which were 12-mm thick in the outgoing M54 engine.
N52 utilizes a revised version of BMW’s Valvetronic variable valve lift technology, varying valve lift to better control engine power without the need for a conventional throttle. The decision to use more rigid reciprocating parts resulted in a maximum engine speed increase of 500 rpm and maximum intake-valve lift has been increased from 9.7 mm to 9.9 mm, helping to boost maximum power output. Engineers redesigned the combustion chamber shape of the N52 to maximize intake-valve phasing to produce a more stable combustion process and improve emission control. Higher fuel injector pressure levels also reduce emission levels during cold start operations. Handling all of these changes required all-new electronics with upgraded calculating capability.
The turbo-charged N54 engine utilizes two small turbos—each supplying three cylinders—to eliminate any concerns in regards to turbo lag and overall durability. Utilizing materials derived from technology used in the space program, the N54’s turbochargers can withstand the most extreme heat from the exhaust stream at upwards of 1920°F. Borrowing the piezo injection technology found on the 760Li’s V-12 engine, engineers were able to better calibrate the delivery of fuel to the combustion chamber, while marginally improving fuel economy 2-3%, improving power delivery and reducing emission levels upwards of 20%.
Even though being the middle child results in gaining a number of hand-me-downs, the 2008 5-Series does manage to get a few cosmetic upgrades to keep it fresh, most notably the new front headlamp treatment, complete with BMW’s signature furrowed brow and a new front air dam design. The rear fascia features a new tail lamp design and a reshaped rear bumper, with a new diffuser design. The cabin has also been redesigned with trim pieces flowing throughout the instrument panel into the doors, providing a more integrated appearance. The iDrive control system has been dumbed down—thankfully—to include six new favorite buttons for easy access to frequently used features, including address book and radio station presets.