A One of the small, high-pressure turbo chargers with variable geometry creates boost during low engine revolutions
This engine just doesn't seize to amaze me and I hope to have the opportunity to have a go at it someday. In the meantime please BMW fit it in a RWD car!!
- Here's an interesting article from Automotive Engineer, lookout for the detail about the cylinder head bolts meeting the main bearing ones.
Sequential boosting is a mature technology now but, when BMW first used it in 2004 to make its straight-six diesel more potent, it marked a step-change in engine development. Connecting one small and one large turbo in series meant that low-end torque and top-end power were both far higher than what the single-turbo 3-litre unit could produce.
Now series- and parallel-sequential boosting systems appear on competitors’ V6 diesels so BMW’s latest offering has been developed to satisfy consumers’ demands for even more power. The solution is a third turbocharger. The company claims this feature is unique and makes this six-cylinder diesel, known in-house as the N57S, the most powerful in the world.
The engine is based on the existing 2,993cc 230kW/630Nm unit, but output has been raised to 280kW and 740Nm – 60Nm more than is achieved by the 4.4-litre gasoline V8 in the high-performance M5. Increasing displacement was not an option – BMW diesels are modular in design and have many shared components – but making everything fit was still tough.
“The first challenge was integrating the technology into the engine and then into the vehicle but our inline layout offers optimum conditions,” says Detlef Hiemesch, BMW’s development manager for diesel engines and exhaust aftertreatment.
“We didn’t modify the bore or stroke because it had to remain part of our engine family – this was a very high priority from the very beginning. So we had to increase robustness to achieve this high specific output – more than 93kW/litre.”
BMW’s engineers had the advantage that they could use the entire right-hand side of the engine to fit in the three turbos, together with a close-coupled oxi-cat and particulate filter housed in the same can. Doing this on a V6 – which has a much shorter block – would be much harder.
The higher ratings meant an increase in peak combustion pressures from 185 to 200bar. Audi and Jaguar diesels use high-strength compacted graphite iron blocks to handle the stresses but BMW’s engine is still all-aluminium. Hiemesch says that cast-iron solutions were considered but would’ve meant that weight targets would be exceeded and would’ve deviated too far from the core design.
So a number of improvements were made instead. A secondary heat treatment process seals any surface porosity in the block castings. Interbore cooling bridges have been improved to help with the thermal loads. But perhaps the most significant change is to the clamping method used for the cylinder head and main bearing caps.
“We had the idea to connect the bolts,” says Hiemesch. “We have a large threaded insert in the crankcase where the cylinder head and main bearing bolts meet. The insert is steel – that’s the key to success.”
The crankshaft and con rods have been strengthened too. The pistons, supplied by Federal Mogul, have remelted crowns to help cope with the high mechanical and thermal loads – the technology is used in Daimler’s V6 diesel too.
- A nice overview of the turbo chargers from Diesel power magazine but also a bit controversial on the ultimate driving machine thing.
B The larger, low-pressure turbo is located on the bottom and joins in with the smaller turbo located directly above it during medium engine speeds
C When the engine gets higher in the rpm band, the final, small, high-pressure variable geometry turbocharger joins in with the other two
D The Diesel catalytic converter is located close to the engine to take advantage of its heat; the oxidation-type converter oxidises hydrocarbons and carbon monoxide using the oxygen present in the diesel exhaust
E The EGR cooler prepares exhaust gases for reintroduction into the combustion chamber, which limits NOx formation
The Ultimate Driving Machine is a Diesel
The only thing we don’t like about the new BMW N57S triple-turbocharged Diesel engine is that it’s not available in the United States. Although it hasn’t physically reached our shores, the idea of a high-performance diesel that can dominate its gasoline challengers in every measurable way has sent shockwaves through the spark-ignited performance community. After the 127hp/liter diesel bomb went off and the dust settled, some automotive journalists with affection for gasoline engines took offence to the diesel onslaught and tried to downplay its high performance numbers by complaining about its lack of noise and unfamiliar feel. Others, such as former Motor Trend editor Angus Mackenzie, get it. And he offered an opposing view, expressed in a 2011 article titled, “BMW’s Best Six Is…A Diesel.” Perhaps the only ones not shocked by this high-performing diesel are the editors and readers of Diesel Power, who welcomed the news as confirmation of something we already knew.
BMW M Performance Diesel
Engine type: All-aluminum 3.0L diesel I-6
Displacement: 3.0L (2,993 cc)
Bore x Stroke (in.): 3.30 x 3.54
Compression ratio: 16:1
Fuel Delivery: Common-rail direct injection (31,908 psi) (2200 bar for us Europeans)
Valvetrain: 24-valve DOHC
Mfg.’s hp at rpm: 381 at 4,000
Mfg.’s torque (lb-ft) at rpm: 546 at 2,000 (that's 740 N.m for us Europeans)
- And of course the compulsory video: