It’s no secret that the automotive world is filled with incredible inline-six engines. Some of the best examples include the Toyota 2JZ, Ford Inline 300, Ford Barra, and so on.
But, it’s hard to deny that BMW is the one that’s actually the king of producing inline-six engines, and in this article, I’m going to explain why.
BMW’s Early I6 Engines
Now for those who don’t know, BMW’s legacy of producing the best inline-six engines goes way past engines like the N54.
As a matter of fact, their history with the inline-six engine design starts all the way back in 1917, before BMW was even BMW.
This is the Rapp Motorenwerke IIIa, which is a massive 19.1L inline-six engine that was used as an aircraft engine supplied to the German military.
This massive thing outputs an insane, earth-shattering 200hp at altitudes all the way up to 2000 meters.
Now to be fair, aircraft engines have always had lower horsepower per liter figures, as that massively helps with engine longevity and reliability.
Because let’s face it, you’d rather not have your engine explode when you’re thousands of feet in the air.
And as you’d expect, it was technologically a dinosaur, with a single-overhead cam design and a 6.4:1 compression, which was actually considered quite high for the time.
This engine was then followed by an even larger 23.5L aircraft inline-six and then later a 22.9L aircraft inline-six.
But, it wasn’t until 1933 that BMW produced their first ever automotive inline-six engine with the M78, which was a little engine series available in displacements ranging from 1.2L up to 2.0L.
After the M78, we saw the M328, M335, and M337. All of these are important to BMW’s inline-six history, but frankly they’re all a little bit boring, so we’re going to skip ahead to 1968 when BMW introduced the M30.
Now, the M30 was introduced following the introduction of the smaller BMW M20 and they were produced alongside each other through the M20’s production.
Back to the M30, though.
This engine was roughly based on the BMW M10 four-cylinder engine, which itself, was the basis of the S14 engine that ended up powering the E30 M3.
Anyways, the M30 engine was part of BMW’s M series, and with that came a few unique and advanced design choices, including an aluminum cylinder head rather than iron and hemispherical combustion chambers.
That’s right, this engine was a Hemi.
One of the most iconic iterations of the M30 engine was the M30B35 found in the BMW 635CSi and 735i. This 3.5L engine produced a respectable, at the time, 218 horsepower and 224 lb-ft of torque.
Ultimately, the engine ended up becoming a staple of BMW’s lineup during the 1980s.
Jumping forward in time, we have the M88 and S38 that came along in 1978 and continued on until 1989.
The M88 was based on the dual-overhead cam version of the BMW M49, which itself was an engine used in BMW 3.0CSi race cars.
And interestingly enough, it was also produced alongside the M30 as more or less a high performance version of the M30.
The important change here is a switch from single-overhead-cam to dual-overhead-cams, which resulted in a pretty large jump in power to 273hp and 243lb-ft of torque in the BMW M1.
Other versions of the M88 include the GR.4 Procar and GR.5 Turbo variants, which produced as much as nearly 1000hp.
I mean seriously, a near 1000hp engine in the early 1980s was pretty ridiculous, especially considering the M88’s displacement of just 3.5L.
In 1984 we saw the M88 replaced by the S38, but only in North America, with the most notable difference being the lower power output.
Why do we always have to get the detuned engines here in America? What did we do to deserve this?
Luckily, a few years later in 1989, the S38 became the global replacement for the M88 and there was a slight power bump.
Now the next two engines I most definitely cannot skip over, as they are BMW’s first ever turbocharged inline-six engines, and that’s the M102 and M106, both of which could only be had in the E23 745i.
Neither of them were particularly impressive in terms of power output at about 250hp for both models.
And it’s important to note that while these were BMW’s first turbocharged inline-six engines, they were not mass-produced.
So, a lot of people don’t really consider them to be BMW’s first turbocharged inline-six engines, and instead give that title to the N54, but we’ll get to that later in the video.
So, up until this point in BMW’s history, they already had a pretty impressive legacy of producing inline-six engines that offered quite a bit of performance while also being reliable, but there’s still so much more to cover.
Jumping forward to the late 1980s we’ll find the engine that replaced the M20 with the M50, which took a massive step forward in terms of innovation with a dual overhead cam setup, coil-on-plug ignition, a plastic intake manifold, VANOS on the later versions, and much more.
But, it wasn’t until a few years later, in 1992, that we saw BMW introduce their high-performance version of the M50, dubbed the S50.
Now this engine made its debut in the E36 M3, which is still known and loved among BMW enthusiasts as one of the best M cars ever built.
And the S50 engine showcased BMW’s dedication to building high performance, high revving, naturally aspirated inline-six engines.
But unfortunately, the US, once again, got the short end of the stick, with the S50 never making its way here.
Now, we did get the S50B30US, but that’s more along the lines of a modified M50 rather than a relative to the European S50.
Later on, though, we did get the S52 here in the States, but that engine was based on the M52, rather than the M50.
And between the two, the S50 is most definitely the more technologically advanced and capable engine.
The S50 features an iron block with aluminum cylinder heads. In its final form, it came with pretty much everything BMW could throw at it, including an advanced double-VANOS system and individual throttle bodies.
Meanwhile, the S52 featured a comparatively weak two-stage VANOS system without individual throttle bodies, plus a lower redline and reduced compression ratio.
Now that takes us to one of the most timeless cars of all time, the E46 M3 and its powerful S54 engine under the hood, which is ultimately an evolution of the M54.
Unlike the M54 though, the S54 uses a heavy cast-iron block which is actually based on the block from the S50 in the E36.
I know it seems weird that the M54 has an aluminum block and the S54 doesn’t, and well, that’s because it is weird.
Realistically, the S54 is more of an evolution of the S50 rather than the M54, but that’s a topic for another day.
Total displacement is 3.2L, which was up from the S50 which was only a 3.0L.
Inside the S54 you’ll find a forged and nitrated crankshaft with twelve counterweights, forged connecting rods, and high compressions forged pistons.
All of this was designed to help the rotating assembly handle the stress of high RPM, with a redline of around 8,000 RPM.
The aluminum, 24-valve cylinder head got a pretty major redesign as compared to the S50’s head.
Not only is the S54 head lighter, but it also includes an improved continuously variable valve timing double-VANOS system, new hollow camshafts, and finger followers instead of the old bucket-style lifters.
One of the more notably features is the individual throttle bodies on the intake, which offer a ton of performance.
This is something we saw on the Euro S50 but didn’t see on the American S52.
All that fancy stuff equals an output of 338hp and 269 lb-ft of torque.
That might not sound like much, but for a naturally aspirated 3.2L engine, this was absurd at the time. Hell, it’s still an impressive figure today.
Anything over 100hp per liter naturally aspirated from an automotive-based engine is an impressive figure in my opinion.
Now that takes us up the engine that many people call the “modern 2JZ” and that’s the N54.
Remember when I mentioned this engine earlier? Well, this is truly BMW’s first-ever mass-produced turbocharged inline-six engine, but mass-produced is the key phrase there.
Up until 2006, BMW was focused on naturally aspirated engines. Cars like the M3 were known and loved for their high-revving naturally aspirated engines which made you work hard for the power.
They debuted the all-new and very advanced N54 at the 2006 Geneva Motor Show and launched it in the 335i.
The N54 is part of the NG6 BMW engine family, and with that, it uses an aluminum block and aluminum head just like other engines in the NG6 family.
The idea behind the N54 was to produce an engine which was super smooth, offered significantly more torque than previous BMW 6-cylinder engines, and virtually no turbo lag.
Of course, doing all of that with a first-generation turbocharged engine isn’t exactly easy, but they did do it, however, reliability was far from ideal.
At the time, that wasn’t a known problem, but today the N54 is known as an engine with quite a few quirks.
Shortly after the N54 came the more evolved and refined N55, which switched to a single turbo system to help with reliability, but it did take a hit on peak power when tuned with a stock turbo system.
And while this is slightly off-topic, it’s worth noting that many N55-equipped cars, such as the 135i and 335i, were equipped with BMW’s dual-clutch transmission, which was leaps and bounds better than their previous automatic transmissions you’ll often find in N54-powered cars.
And built of the N54 and N55 platform came one of BMW’s best performance engines ever, the S55, which is the engine that powered the F80 M3, F82 M4, and later on, the M2 Competition.
And of course, that’s a big claim, but out of all of BMW’s incredible inline-six engines, it’s hard to argue that the S55 isn’t the best of them all, at least in the context of aftermarket performance.
Now starting with the basics, the S55 is based on the N55 we just talked about, but with a focus on massively improving the performance and reliability when it comes to track use.
But, unlike the N55 which used a single turbo setup, BMW switched back to using a twin turbo setup with the S55.
Now this was likely done because BMW just simply couldn’t reach the power levels they were chasing while also keeping turbo lag to a minimum and maintaining a relatively flat torque curve.
Now depending on the application, power output for the S55 ranges from as low as 404hp in the M2 Competition all the way up to 493hp in the M4 GTS.
But, the stock power output isn’t what makes the S55 such an incredible engine, but rather all the power BMW left on the table.
With that twin-turbo system and the much-improved fueling system as compared to the N55 it’s based on, the S55 is capable of producing over 550whp and nearly 600wtq without modifying the turbos or the fuel system.
But it gets even crazier than that.
With an upgraded turbo and fuel system, the S55 is happy to make over 700whp on a completely stock bottom end and transmission, with some tuners taking the S55 as high as 1200whp, which is close to 1500hp at the crank depending on how much drivetrain loss you want to factor in.
Now if you don’t know what any of those numbers mean, it simply means the S55 can make ridiculous amounts of power when modified.
BMW took a page out of the 1990s Toyota book and really overbuilt the S55. It’s an engine that’s happy and very capable of making something like 700hp at the crank while maintaining excellent drivability, a fantastic power curve, and a highly response dual clutch transmission behind it.
Now it is worth mentioning that the S55 isn’t a perfect engine and the most notorious problem of them all is actually pretty serious and that’s the crank hub which has a tendency to spin off the crank and cause some serious damage.
The problem is that BMW designed the OEM crank hub with two gears, one of which is for the timing system, but these gears have the ability to spin separately if enough torque is applied to them.
If the crank hub spins, it can alter the valve timing and if you’re unlucky enough, it can cause piston-to-valve contact and grenade the entire engine.
Luckily, there are plenty of aftermarket solutions that solve this problem, but it’s something that was worth noting.
That takes us to 2020 when BMW launched the G80 M3 and its hideous front end.
Seriously though, why does this thing look like a pig from Angry Birds?
On a more serious note, the S58 follows in the footsteps laid by the previous engines, with a 3.0L displacement and twin turbos strapped to the side of it.
Of course, it’s also worth mentioning that the S58 is based on the B58, the engine found in the A90 Supra, and while that is a good engine, it’s not particularly amazing or groundbreaking in terms of performance or innovation.
So if you want more info on that engine, we’ll leave some links to our other videos covering the B58.
Back the S58 though, what makes it such an incredible engine is much of what makes the S55 an incredible engine, the pure performance that its capable of with aftermarket parts.
The S58 hasn’t been available for a particularly long time, but tuners have already pushed it pretty far.
In totally stock form, the S58 puts down around 473hp and 442 lb-ft of torque, which is already an increase of 48hp and 36 lb-ft over the previous S55.
The Competition models will push that even further, with an additional 78hp over the standard S55 and still 10hp over the beefed up S55 in the M4 GTS.
With some basic bolt-ons and ethanol fuel, we’re already seeing S58 engines making upward of 650whp and 650 wheel torque, and some pro-tuners are getting close to 700whp.
You heard that right, upwards of 700whp, which is something like 850hp crank horsepower, on a stock engine with stock turbos.
This is a 3.0L engine, that kind of power output from bolt-ons and tuning is quite literally unheard of for an engine this size.
For reference, a bolt-on S55 running on ethanol fuel will generally see a max of 600whp. And compared to the S55, the S58 has larger turbos, a lower compression ratio that is more friendly to increased boost levels, an improved fuel system, and a one-piece crank hub design that doesn’t explode.
With some fueling modifications and larger turbos, some tuners have already pushed the S58 to over 1000hp reliably, all while using a stock bottom end.
And with all that power, we’ve already seen some S58-powered cars get into the 8-second range down the 1/4 mile. I’m not a fan of the term “modern 2JZ”, but the BMW S58 is arguably the best inline-six since the Toyota 2JZ.
Individually, I think you could certainly make a case for the Ford Barra or Toyota JZ as being the best performance inline-six engines ever.
Or the Jeep 4.0L or Ford 300 as the most indestructible inline-six engines ever, but I think it’s fair to say that BMW is the king of it all.
They’ve produced so many incredible inline-six engines throughout the decades and they’re still building amazing inline-six engines to this day, something that almost no other automotive manufacturer is doing, other than companies in the diesel engine world.
When it comes to gasoline powered inline-six engines though, BMW is the king. But, go ahead and prove me wrong in the comments down below.