It’s been a long time coming, but after years of speculation, hope and fear, BMW’s M division has launched their first Diesel cars/SAVs. As if to apologize for the lack of spark plugs, the marketing gurus have branded these new M Diesels as “M Performance Automobiles.” We’re hard at work trying to determine if this is a cypher with encoded meaning. Here’s what we know about the new M diesels so far, and why they may be slightly sub-branded from the M division.
A matter of redline.
The heart of an M car is always its engine. Historically, M cars have had hearts that beat very fast – as in 8,000 + rpm; in the medical community we’d call that ventricular tachycardia. In the BMW community, we call that spinning to heaven. Predominately due to the specific burn rate of diesel fuel, compression-combustion engines (diesels) cannot rev as high as sparked (gasoline) engines. Most diesel engines in the automotive market today rev to a maximum of 4,000 to 4,500 rpm. Above 3,000 rpm, most of these diesels will sound and feel like they are about to spin themselves to oblivion, becoming rash, noisy and a bit unhappy. BMW diesels, however, welcome revs – whatever their redline might be. In the case of the new M diesels, redline is set to a maximum 5,400 rpm. That may not sound very high in the company of high-revving M engines, but trust us: for a diesel, that is stratospherically high.
Consider that modern turbo-gasoline M engines – such as the S63tu engine found in the new F10 M5 – rev to a maximum 7,200 rpm, and this high-revving diesel appears that much more impressive. The new M diesel gives up only 1,800 rpm to the highest revving turbo-gasoline M engine, and produces prodigious power along the way. This diesel, ladies and gentlemen, is an engineering marvel, a technological masterpiece. We will lay down the farm to bet it will win multiple engine of the year awards. This 3.0 liter turbo diesel is a genuine M engine – let’s get that matter out of the way early on in this tech piece.
One turbo, two turbo. Two turbo, three?
Did somebody say three turbos? Isn’t that kind of a lot of turbos? Indeed it is, and we don’t mind one bit that there are six scrolls packing air into six cylinders in a row. In fact, we rather like the concept and feel it’s a touch exotic. It’s the V-12 of turbos if you will. Lots of turbos – not cylinders. We haven’t had all of the technical information released to us yet, but from what we know so far, the turbo setup on this new diesel M engine is the most advanced turbo layout M – or any other car company for that matter – has ever produced for a production car.
With three twin-scroll turbos fed by and in-turn charging six cylinders, M have dedicated every cylinder to feed one scroll each. We do not have this detail yet, but we imagine all three turbos are of different sizes, a small turbo to spool up quickly at low rpm and provide instantaneous boost, a medium sized turbo to handle mid-rpm, and a very large turbo to produce maximum boost at high rpm.
As if this setup was not impressive enough, each turbo features variable-vane geometry (think Porsche 911 Turbo, though BMW Diesels have long featured this technology) and this allows each turbo to more efficiently spin-up and produce maximum boost across the entire rev-range. That word, “exotic” is once again coming to mind.
Don’t get your fingers near the fuel injectors… not that you would.
You’ll be too busy driving, of course. And for the health of your fingers, that’s a good thing because the piezo injection pressure of M’s new diesels would take your fingers clean off. Fuel is injected at a staggering – are you ready for this?- 2,200 bar. That’s equivalent to 31,908 psi. That is a mind-blowing figure – I’ve simply never heard of such a thing. The highly precise metering and timing of fuel injection allows for improved power, efficiency and responsiveness – extracting every joule of energy possible from every micro-droplet of diesel fuel.
Add more lightness, please.
The M engineers have not disappointed in the area of weight, using light-weight materials as much as possible in the engine. For example, the crankcase – which is normally made of heavy-duty steel to withstand the forces at play – is made of aluminum to stave off weight. We do not have final figures on the total wet weight of the engine, but we can’t wait to find out. We expect the engine block and head to also be constructed of aluminum, significantly lightening the engine. A lighter engine will allow for quicker chassis responses and more nimble, agile handling. The lower weight will also add to the balance of the car, ensuring no more than 50% of the weight rests upon the front axles.
Higher specific-output than the M5(!)
These figures caused me to do a double take, and then sit back in my chair for a moment with eyes glazed over – in mad fascination. As a reminder, the M5′s S63tu unit measures 4.4 liters in displacement, and produces 560 hp from 5,750 to 7000 rpm and 501 lb-ft of torque from 1,500 to 5,750 rpm. The new 3.0 liter M diesels produce 381 hp from 4,000 to 4,400 rpm and 546 lb-ft of torque from 2,000 to 3,000 rpm. That means a specific output of 127 hp/liter and 114 lb-ft/liter for the M5 and – paint me red and shoot me dead – 127 hp/liter and 182 lb-ft/liter for the M diesel. Theoretically, if the M division increased this Diesel’s displacement to 4.4 liters while keeping the same specific output, it would match the M5′s 560 hp while producing more torque – a gluttonous 801 lb-ft.
Yes, you read that correctly, the M diesel actually has superior specific output to the M5. Give your head a shake and start clapping – I don’t care where you are right now – seriously start clapping, slow and loud. Your workmates, family, or fellow shoppers will eventually understand when you give them a ride in your new M diesel.
3 tenths off the M5.
The M550d xDrive sedan will reach 60 mph in only 4.7 seconds, giving up only 3 tenths to the M5. True, various automotive outlets such as Car and Driver have achieved much faster acceleration times for the M5 – as quick as 3.7 seconds to 60 mph. But we’re quoting factory claimed times for both cars, so we expect the M diesel will shave time off of the claimed figure as well.
All of this with hybrid levels of efficiency?
The story just keeps getting better. As if the performance alone wasn’t enough reason to put an M diesel in your driveway, the efficiency should seal the deal. When bolted into the F10 5 series chassis, the diesel will manage 6.3 liters/100 km (44.8 mpg) in the EU test cycle. Consider that the Toyota Prius manages 64 mpg while boring you nearly to death and barely getting you there on time, and the M diesels make a compelling case for themselves.
M Diesel? Bring it on.
We are tickled pink by the release of the new M diesel engine and we positively cannot wait to interview M engineers to learn more about it. Of course, we are even more excited to drive the new line of M diesels just as M cars were meant to be driven: flat-out and a little bit sideways.
Four models have launched with the new diesel engine: the M550d xDrive Sedan, M550d xDrive Touring, X5 M50d and X6 M50d. The claimed accelerations times are 4.7, 4.9, 5.4, 5.3 seconds respectively.
Finally we arrive at the question: why label these diesels under a slightly partitioned off sub-brand? It appears that the character and intent of these cars will be unique from the gasoline powered M cars, while putting out similar performance. The fact they were developed in-house by M proves they are indeed proper M cars. But for now it appears M is distancing them slightly from the rest of the lineup while fans and owners around the world warm to the concept of a Diesel M. I don’t know about you, but we’re already hot under the collar.