This bit of news won’t affect most drivers in the US market, but it’s interesting just the same. BMW makes an M version of its largest luxury sedan that is powered by a diesel engine. The current 750d uses a 3.0 liter in line 6 cylinder engine with three turbos. Now the company says it will add a another turbo to the mix, bringing the total to 4. The new engine not only increases power, it also uses significantly less fuel.
The importance for drivers in America is about how those clever mechanical engineers continue to delight and amaze us with ways to keep the internal combustion engine relevant, despite the challenges from electric cars. Who knows if there might be cars with multiple turbos offered to American drivers in the future?
The new engine is rated at 400 horsepower — a 5% increase. It offers 560 lb-ft of torque and BMW says 332 ft-lb of that is available immediately at idle. Even with such impressive power, the new engine is capable of returning 49.6 mpg in the admittedly generous UK test cycle.
In this latest BMW oil burner, two compact variable geometry turbos built into one housing handle high pressure demands by spooling up quickly and providing instant boost. In BMW’s existing tri-turbo motor, these small turbos worked in tandem with one big low-pressure turbo, but that has now been replaced by two smaller units for faster response.
In normal operation, only the two low pressure turbos and one of the high pressure turbines will be active, but when you whistle down to the engine room for maximum power by placing your right foot firmly on the go pedal, both high pressure turbos are called into action. The larger low pressure turbochargers are bypassed to let the boost build quickly. Thanks to all this shuffling of turbos going on under the hood, the sedate BMW hustles to 62 mph in a decidedly unruly 4.6 seconds.
All of this boosting and bypassing is managed by BMW’s latest Digital Diesel Electronics controller. It manages each turbocharger, the position of the variable geometry turbine vanes, the position of the flaps that allow each turbine to be bypassed or called into action, the exhaust gas butterfly valve, the wastegate, and intercooler.
The engineers responsible for this latest engine have added a new five layer head gasket, low friction coatings on the cylinder bores, and pistons made from an alloy of aluminum and silicon. The 750d xDrive will be available in regular or long wheelbase versions. It is expected in showrooms in June.
Source: Gizmag Photo Credit: BMW