Finding an alternative to a large displacement diesel engine that produces impressive power figures is no easy task. For one reason or another, it just never works out. Take the BMW B57S engine for instance. While it may have been removed from the product lineup way back in the autumn of 2020, the quad-turbo BMW B57 turbo-diesel engine was a pretty wild feat of engineering.
Wild, not just because it came fitted with four spinning snails, a compact 3.0-liter inline six-cylinder blueprint, eyebrow-raising performance figures, and equally impressive efficiency ratings. These considerations were but mere selling points, for there was something far more important that BMW had to contend with at the time.
Despite all of its perks, the BMW B57 quad-turbo diesel engine faced an uphill battle from inception. And like so many other brilliantly bizarre engines that came before it, this boosted European oddity found itself labeled for elimination not long after its release. A victim of the times, if you will.
Which makes us wonder… what if BMW was really onto something with this force-fed quad-turbo engine design? What if it was just a bit ahead of its time? That, or perhaps it was just a decade too late?
One Big, Weird Supra Diesel Engine
From a genetics standpoint, the B57S quad-turbo diesel was a bit more of a spliced-gene experiment than anything. As an upsized (and ultra-expensive) offshoot of BMW’s family of new inline six-cylinder engines, this powerplant relies upon many of the same base genetics as the B58 engine powering the resurrected Toyota Supra.
That means it shares many similarities with BMW’s far more bland B38 and mid-range B48 gasoline-powered engines, along with their Deutsch diesel doppelgangers, the B37 and B47. All of these share an individual cylinder displacement rating of 500cc, an aluminum block and head, four valves per cylinder, and the unrelenting sex appeal of a soggy plate of day-old schnitzel.
However, it is the B57D30S0 engine that is the real freakshow within the fold, for it is the engine that contains ALL ZEE SCKNECKEN.
Deutschland’s Diesel Wars
Originally intended to power BMW’s lineup of sedan-shaped land yachts, as well as a select few larger SUV offerings with equally hideous beaver-tooth grilles, the quad-turbo B57D30S0 diesel engine is built for moving some serious weight at more than a snail’s pace.
Never intended for the American market, this European exclusive came to life after a German competitor began adding more than two turbos to its larger diesel engines. As rumor has it, it was Audi that ruffled BMW’s leathery lederhosen laces, when it announced its triple-compressor TDI engine for the SQ7 SUV. Two turbochargers, one electric blower, and virtually zero turbo lag.
So naturally, BMW decided to do what any respectable automaker would do: It got in a forced-induction pissing match with its German rival and unloaded all the spool it had been saving up, all at once.
Designed with a dual multi-stage setup in mind, the B57S motor relied upon a set of smaller, low-pressure twin-turbos for low-end boost, and a separate set of larger snails for handling high-flow efficiency. This resulted in wig-splittingly impressive transient power response rates, with almost zero turbo lag down low, and plenty of pull up top. The latter of which, as we know, tends to be where most diesel powerplants typically fall flat.
From a rotational standpoint, the two smaller, variable-vane turbos remain in motion at all times. Additionally, one of the larger units spools up alongside the two smaller units, leaving the other larger snail to remain dormant until the throttle hits the floor. At which point it kicks in full force, and away your land yacht sails down zee Autobahn.
To achieve figures that were potent enough to move BMW’s heavy hitters, around 394 horsepower and 561 lb-ft of torque were produced by the B57D30S0 diesel motor. Without question, these are impressive figures for a 3.0-liter inline sixer. Statistics that are only matched by a 41-mile-per-gallon average.
On top of this, a 48-volt starter generator, or “mild hybrid support system” was added to help reduce lag and achieve peak torque from 2,000-4,000 rpm, as peak horsepower landed right at 5,000 rpm. Predictably, BMW marketed this electronic hybrid assist generator as a way of making this motor more “green,” when in actuality it didn’t help the engine whatsoever when it came time to clear emissions.
The Downward Spooling Quad Turbo Spiral
As fate would have it, the B57S engine was first put into production in 2016, at a time when the word “diesel” was synonymous with emissions-cheating scandals and German automobiles. So yeah… not the most opportune time to launch something like this, even if it was intended purely for the European market.
But BMW plowed onward with production, focusing on outfitting its largest sedans and SUV platforms with the B57S engine. And guess what? It sold. Not like Marzen bier at Oktoberfest sort of sales figures, but in numbers that were respectable enough to warrant keeping the engine in the lineup. At least for a while.
However, come the COVID pandemic, that dreaded double whammy of increased production and material costs materialized. Compounded by a fresh round of über strict EU emissions regulations, and it became damn near impossible to justify the quad-turbo B57’s presence in the BMW portfolio.
From an aftermarket performance viewpoint, this engine proved to be quite the prude too. While the engine’s trick piezoelectric injectors allowed ten injections per engine cycle, thus boosting efficiency and power, mandatory emissions add-ons bottlenecked the true capabilities of this motor at every turn. Massive exhaust gas recirculation valves, diesel particulate filters, oxidation catalysts, diesel exhaust fluid injections… it all added up to one thing. Muted power.
But it was the 95 grams of CO2 per kilometer regulations mandated by the Euro 6d emissions standards that proved to be this engine’s arch-enemy. Since one of these units produced anywhere between 154-163 grams of CO2 per kilometer on any given day going down Zee Autobahn, an executive decision had to be made. The B57S engine needed to be removed from production.
It would have been insanely expensive (and power-robbing) for BMW’s engineers to get this quad-turbo diesel engine to the point where it would pass inspection. And so the B57 was discontinued just a few short years after takeoff due to its inability to meet these new emissions restrictions. BMW was not alone though, as a few other larger diesel motors from competing German companies, including Audi, were also scuttled.
Final Edition models of the X5 M50d and X7 M50d for Eastern and Central European markets — the prior which was a platform that weighed nearly 2.5 tons without any passengers aboard — hit 62 mph in just 5.2 seconds thanks to the help of the utterly over-engineered B57S engine.