BMW S55 vs S58: Which One is Better?

In a world of turbocharged four-cylinders, hybrids, V6s, V8s, and electric drivetrains, BMW is the only manufacturer who has stuck with the inline-6 engine layout. Most manufacturers dropped their inline-6 engines long ago for a variety of reasons, and even BMW did drop their inline-6 engine in their flagship sports car, the M3. Of course, that was the E90/E92 generation of the M3 where they moved to a V8, but they have since moved back to inline-6 engines.

In the F80/F82 generation of M3, we saw the S55 which was effectively a done-up version of the N55. Now BMW is moving to the G80 M3, and this new version of the M3 is sporting the new S58 engine, which is a hopped-up version of the B58. Now the question a lot of enthusiasts have, is the S58 better than the outgoing S55, and did BMW make the right decision basing their new performance engines off the B58 instead of the N55.

Well, let’s dive in and compare these two to see which one is better.

Where Did Each Engine Come From?

Before we get into this, yes I know the S58 is already being used in the X3M and X4M, it’s not just exclusive to the new G80 M3/M4 platform. With that out of the way, let’s take a quick look at the S55 and what makes it a special engine.

The S55 came onto the scene four years after the introduction of the N55. The introduction of the S55 was a really interesting move by BMW because, as we mentioned in the intro, the E90/E92 M3 used a V8 engine rather than BMW’s traditional inline-6. For them to go back to an inline-6 engine from a V8 was a sign of them acknowledging what a lot of their customers wanted.

Cylinder Heads, Turbos, and More

When you boil it down, the S55 is just a high-performance version of the N55, meaning it carries a lot of similar parts and designs from the N55. According to BMW, the N55 and S55 share about 75% of their components and the remaining 25% of the components were new developments.

The important changes BMW made when going from the N55 to the S55 are a closed deck block, twin turbos, forged pistons, lightweight crankshaft, and dual high-pressure fuel pumps.

In terms of design, the S55 cylinder head flows pretty well, especially for a direct-injected turbocharged cylinder head. The important things that make the S55 such an awesome engine are the OEM turbochargers, which are two mono-scroll turbos, each of which has cast-in exhaust manifolds.

With this system, each turbo has its bank, meaning each turbo is powered by three cylinders. Paired with that system is a really capable fuel system that flows a lot more fuel than the N55’s fuel system. On top of that, the bottom-end uses a closed-deck block for extra rigidity and a really strong rotating assembly. When I say strong, I mean people are making 700whp without the rotating assembly.

When it comes to reliability, the S55 is a pretty reliable engine, especially compared to earlier BMW turbocharged engines. On pre-2016 engine models, the crank hub was complained to be a high-failure point, resulting in a spun crank hub, but that issue was and is blown out of proportion by compares looking to sell more crank-hub repair kits.

Outside of this overblown issue, the S55 is a pretty bulletproof engine. The common BMW issues still exist, such as high-pressure-fuel-pump failure, excessive carbon build-up, etc. but overall, it’s pretty reliable, which is not something BMW is historically great at doing.

BMW S55 Engine Specs

  • Stock Power: 425hp / 406tq (different versions have anywhere from 405hp-493hp)
  • World Record HP: 1,150whp (approx. 1,350 crank hp)
  • Displacement: 2,979cc (2.979L)
  • Turbocharger: Twin “single-scroll” turbos
  • Compression: 10.2 to 1
  • Bore x Stroke: 84.0mm (~3.31”) x 89.6mm (~3.53”)
  • Internals: forged steel crankshaft, forged aluminum alloy pistons and rings
  • Block Design: Closed-deck
  • Redline: 7,500 rpm
  • Injectors: Bosch solenoid style direct injectors

Now that you have a basic idea of what the S55 is all about, let’s take a look at the S58.

While the official release won’t be until Q4 2020, it’s no secret that the S58 is being looked at closely by BMW enthusiasts who have gotten used to the insane performance the S55 is capable of. While most of us are waiting to see it in the G80 M3, the S58 has already hit the streets in the 2020 model year X3M and X4M models. It’s based on the B58TU engine, and from the outside looking in, the S58 looks very similar to the S55 for the simple fact that it’s a 3.0L twin-turbocharged inline-6 engine.

BMW S58 Engine Specs

  • Stock Power: 473hp / 503hp and 442tq (503hp is for Competition models)
  • World Record HP: Unknown (for now)
  • Displacement: 2,993cc (2.993L)
  • Turbocharger: Twin “single-scroll” turbos
  • Compression: 9.3 to 1
  • Bore x Stroke: 84.0mm (~3.31”) x 90.0mm (~3.54”)
  • Internals: forged steel crankshaft, forged pistons and rods
  • Block Design: Closed-deck
  • Redline: 7,500 rpm
  • Injectors: Bosch solenoid style direct injectors

Aftermarket Performance

Because the S58 hasn’t been out for very long, there aren’t many performance mods out there yet. That being said, tuning software is already available for the S58 and it’s capable of a pretty big amount of power, especially when tuned on ethanol. In 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 standard 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’s making upward of 650whp and 650 wheel torque, and some pro-tuners are getting close to 700whp. For reference, a bolt-on S55 running on ethanol fuel will generally see a max of 600whp.

Of course, these numbers vary widely from car to car, with different mods, tuners, and fuel, and dynos should not ever be used to compare the power of two different vehicles. Dynos are only good for measuring the delta on one vehicle in the exact same conditions.

That being said, the S58 so far has shown that it’s more capable than the S55 with bolt-ons and tuning. I mean think about it, we’re talking about a stock engine with stock turbos making nearly 700whp with some easy bolt-ons, ethanol, and tuning. That’s insane and would’ve been nearly unheard of 15 years ago.

Again, since the S58’s have barely hit the road so far, we can’t really provide any definitive opinions on reliability because of limited data. We can look at the trend BMW has made, where the N54 was unreliable, then N55 was a bit better, then S55 was a bit better, then Toyota helped BMW with the development of the B58 so that’s been better than the S55, so it’s safe to assume the S58 will be more reliable than the S55. At the end of the day, it’s based on the B58, and so far that has been a very reliable and capable platform.

As always though, you can probably expect a few common BMW problems including the high-pressure-fuel pump, oil filter housing, valve cover gasket, water pumps, etc. As more S58s hit the road and rack up miles, we’ll see how reliable they remain.

Which One is Better?

So, looping back around. Comparing the two engines we see a lot of similarities: twin-turbos, 3.0L inline-6 design, direct injection, forged bottom end, and overall they’re both insanely strong. At the end of the day though, they’re very different engines. The S55 is based on the N55 and the S58 is based on the B58. They’re completely different engine families, although they’re closely related.

Based on the data we have now, it’s looking like the S58 is the better platform. It’s making more power with bolt-ons and tuning, it should be more reliable in theory thanks to Toyota’s involvement with the B58, but right now we don’t which one is better when pushed to the limit, but even that is looking like it’s going to be the S58.

For some of you, this might seem expected, after all, why would a manufacturer like BMW make their engine worse than their old engine, but truth be told you see that all the time. BMW is outdoing themselves and not catering to the fuel-efficient eco-minded customers. They’re building cars and engines for enthusiasts and really not cutting any corners.

I’ve heard people called the N54, N55, S55, and B58 the “modern 2JZ” and while that name is a lot to live up to, the S58 is probably the closest thing we’re ever going to have to a modern 2JZ.

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