I can feel metaphorical pitchforks being thrown at me as we speak. Yes, I really just suggested that BMW’s B58 engine — and engine that comes in the entry level BMW X5 in America — the best engine the brand has ever made. Yes, that sounds a bit extreme at first but hear me out.
The BMW B58 engine is a remarkable one. Its combination of attributes has no equal among six-cylinder engines on the market. In fact, it may not have an equal among all engines on the market. It’s that good. Good enough to suggest that it’s better than all of the glorious BMW engines that came before it? I’m going to say so, though with a caveat. I’m excluding ultra-rare engines such as the S70/2 V12 engine from the McLaren F1. Only mainstream production engines are included.
What is the B58?
For those not consumed by the nerdome BMW enthusiasm, allow me to introduce the B58 engine. It’s a 3.0 liter turbocharged inline-six engine that powers everything from the BMW M240i, to the aforementioned X5 xDrive40i, to the BMW 745e plug-in hybrid. Which leads me to its first attribute.
BMW stuffs the B58 engine into almost anything it can. That’s not unusual in and of itself, as automotive engine homogenization isn’t anything new, from any brand. However, the B58’s breadth of ability is staggering. It powers genuine performance cars, such as the M240i, M340i, X3 M40i, and the Z4 M40i. It also powers standard luxury cars, like the BMW 540i, the X5 xDrive40i, and it’s even good enough for the massively heavy X7 xDrive40i. And it’s even smooth enough and efficient enough to be used in plug-in hybrids, such as the BMW X5 xDrive45e and the 745e.
Sure, there are a lot of engines on the market that hold multiple jobs but none of them excel at every single one like the B58. In every application, the B58 engine feels perfect; as if it’d been built for the sole purpose of being used in that very car. Drive the BMW 745e and it’s almost impossible to tell that its engine could be used a zingy, thrilling, engaging performance car engine.
When it comes to the fun stuff — performance cars and such — the BMW B58 engine is an absolute joy to use, mostly because of its power. In its M Performance spec (all of the aforementioned M40i models), it makes 382 horsepower and 369 lb-ft of torque. On paper. In the rear world, it feels like it has 100 more horses than that. Its pulling power is immense, capable of making even heavy SUVs properly fast.
But it’s not just the power itself but its delivery. There’s torque everywhere in the rev range and virtually no turbo lag. Stomp the go-pedal in any gear, at any rpm, and the B58 explodes, with a seemingly endless surge of power. Driving any car with a B58 engine feels genuinely special, due to the performance waiting at your right foot. Drive any other six-cylinder engine in its class, from any other manufacturer, and you’ll soon realize just how special the B58’s power delivery is.
You’d think and engine with instant response, zero turbo-lag, and damn-near 400 horsepower would feel violent and rough. But the B58 doesn’t. It’s as if it replaced its motor oil with heavy cream. There’s no negative NVH to speak of, with just smooth, effortless delivery. Even at full chat, with revs climbing toward their limit, the B58 never feels anything but smooth and sophisticated. It’s the Captain America of high-revving engines — it can do it all day.
It also works perfectly with the ZF eight-speed automatic transmission. BMW’s engine and transmission calibration might be the best in the business, second to maybe only Porsche, and the B58’s inherent smoothness has a lot to do with that.
Noise and Character
There are a lot of very effective engines on the market, even in the B58’s price range. Audi’s 2.9 liter twin-turbo V6 comes to mind, Alfa’s V6 of the same displacement, and even Cadillac’s new twin-turbo V6. However, none of them can match the character of the B58, with its raspy, metallic exhaust note. All three of which, by the way, make more power and are offered in more expensive performance cars.
Is the BMW’s B58 the best engine in the world? No, of course not. However, BMW’s ubiquitous inline-six has one trick up its sleeve — value. The B58 is available in cars that are affordable to a wide variety of enthusiasts. If you want a more special engine, you need to spend a lot of extra money on the car it comes in. The BMW M240i is under $50,000 and the M340i is under $55,000. You don’t have to spend a fortune to get an engine that feels more special than most other engines on the market.
The only other six-cylinder engine that can beat the B58, in terms of sound, character, power, and feel, is Porsche’s 4.0 liter naturally-aspirated flat-six, from the Cayman GT4. However, that car is far more expensive and that engine is limited to only super special edition cars.
In my own opinion, even BMW’s S58 engine, the M Division version of the B58, lacks the refinement of its less expensive sibling. I also like the sound of the B58 more, as it’s a bit purer and less artificial sounding.
BMW has made a ton of great engine over the years. Its four-cylinders from the ’60s were excellent for their time, the six-cylinders that powered BMWs in the ’80s and ’90s were brilliant, and some of its V8s and V12s were killer, too. However, I honestly don’t think a single engine the brand has ever made has ever matched the B58’s combination of power, performance, refinement, versatility, and price. The internal combustion is going to be a dinosaur sooner than later, so we should all celebrate the pinnacle of the technology and the B58 is just that.