Let me grab my flame suit in advance as I have a feeling this may turn ugly rather quickly. When it comes to modern BMW engines (lets define modern as engines produced by BMW after the year 2000) there are two engines that stand out to me. Two engines that hopefully represent the future of the “Ultimate Driving Machine”, and likely automotive engines as a whole. The naturally aspirated folks are going to kill me – BMW’s best modern engines are the N54 and S55.
Natural Aspiration is Dead
To get this out of the way, I am in no way disrespecting naturally aspirated (n/a) BMW engines. I would own a naturally aspirated BMW well before most other n/a motors. However, natural aspiration is antiquated. It is dead to me, and it is certainly dead to modern performance cars. One frustrating complaint I frequently see regarding newer BMW engines is something along the lines of, “But it’s not naturally aspirated. It has no character.” Maybe this resonates with others, and I would love someone to explain this to me. I fail to see why a turbo engine can’t have as much, or more, character than a n/a engine.
My N54 certainly has a unique character. Every time I let it loose the N54 eats it up, and seemingly begs for more. When I finally go back to normal driving worried its had enough, I just picture my engine laughing at my concern as it has yet to even break a sweat. The sound with catless downpipes and dual cone intakes is intoxicating; it is a unique sound at each RPM and throttle input. Quiet during normal operation, yet a moderate deep note in the midrange followed by a smooth, higher pitched note as it reaches for the redline. Add in the noises from the dual cone intakes and it is truly a unique, enjoyable turbo engine. Some days my N54 runs better than others; the engine certainly informs you when it is ready to conquer the world, or rather, when it would prefer to merely dust a few Mustangs around town. If that is not character, maybe I am simply lost in the world of automotive engines.
Character aside, turbo engines are a brighter future for engines. With emission laws constantly evolving and becoming stricter, one of my greatest concerns is a future filled with boring electric, self-driving vehicles. We may complain about the underwhelming sound of the S55 now, but in 20 years we might be willing to do anything to hear that sound again. Worry not, as BMW is pushing the envelope of high performing, fuel efficient, low emission turbo engines.
BMW May Be Making the Best Turbo Engines in the World
Often, I wondered if BMW kind of messed up with the N54; did they accidentally raise the bar too high for future turbo Inline 6’s? The N54 was BMW’s first attempt at mass producing a twin turbo, direct injected engine. It made its debut in the mid-range 335i, rather than the coveted M3 presumably to work out some early kinks. From its initial release, tuning development only took a few years before a simple tune and a few bolt-ons made it more powerful than an S65, the 4.0L naturally aspirated V-8 found in the E9x M3.
BMW N54 Tuning Capabilities
As the years passed, further advancements to tuning and modifying the N54 came around and shattered most everyone’s expectations. It dawned on me the other day how much N54 owners, especially myself, take their engines for granted. I found it enlightening to read through some old forum posts regarding the N54’s capabilities. There was not only a lot of excitement in the early days of the N54, but also plenty of concern regarding the reliability, longevity, and upper-limits of the engine. As people began pushing closer and closer to 500whp many thought the N54 was nearing the edge before we began to see countless blown motors. Afterall, an open-deck block design and cast pistons on a small 3.0l engine shouldn’t be able to handle much more, right? Nope, it can. The N54 just kept going and going.
The upper limits appear to be in the 700+whp range although it is still tough to say. There is no doubt, at those power levels you better have an excellent, conservative tune with the right supporting mods. Regardless of the specific upper-limit, it’s high. Incredibly high when considering the cast pistons and open-deck block. And it’s not just the upper limits of the factory block and internals that make the engine so impressive. It’s the whole damn N54. I mean everything. From the stock fueling back to the stock automatic transmission that can handle 500+whp and torque. The tiny stock turbos capable of making numbers in the low 500s. Of course, some components have their weaknesses and the risk of blowing the stock turbos increases with power. Nonetheless, my point remains - that is a lot of power for a 3.0l inline-6.
BMW N54 Reliability
Maybe I’ve been lucky, but it’s absolutely stupid how hard I push my N54, yet it keeps running like brand new. I am completely speechless, and mind blown. My N54 has been running a JB4, catless downpipes, and dual cone intakes for about 5 years and 35,000 miles. I’ve experimented with MHD back-end flash tunes, and frequently run a 25-35% E85 mixture. It’s had its issues over the years, but overall, the issues have been minor, and the car has been cheap to maintain. That is incredible given how hard I’ve driven an engine that has been running with roughly 50% more power than in stock form, all with 110,000 miles. I cannot count the number of times it has seen 130mph+, nor the number of times I’ve launched the car hard from a dig.
The conclusion: BMW made one hell of a turbo engine in the N54. Powerful, capable, and reliable. Was it an accident that raised the bar too high, or can BMW just build one hell of a turbo inline-6?
The BMW S55
It turns out BMW may not have set the bar too high at all – enter the BMW S55. Building off the basic design of the N54 and N55 engines, BMW seems to have nailed the S55. The engine is still relatively new from a tuning perspective. Things take time to develop in the early years for obvious reasons. It takes time to crack the ECU and tune the engine. Further, many cars are under warranty for the first 4-6 years, and not many owners are willing to risk voiding the warranty with aftermarket modifications. Yet, on paper, the S55 should crush the accomplishments of the N54. It is certainly already showing a lot more potential on stock turbos.
What Are the Upper Limits of the S55?
It’s far too early to know for sure, but we can examine what we currently know. The S55 on stock turbochargers can make well above 500whp and 550wtq with a JB4, a few bolt-ons, and some E85. Toss on a set of Pure turbos and the S55 is able to make well over 600whp. There are already a few built-motors running over 1000whp, however, I don’t want to include those examples as I am more interested in what the S55 can do on stock components. Right now it is all a guessing game, but we do know the stock components can handle into the 600+whp territory. What’s most impressive is the fact the engine is doing this on stock fueling, stock turbos, and an un-opened engine. Seeing as the N54 can handle over 700whp on cast pistons and an open-deck block, I do not think it is unrealistic to expect 800-1000whp on the S55. Again, that is nothing more than a guess based on the stronger engine design of the S55 compared to the N54. It will take time before enough people are testing the true upper-limits of the S55. However, 600whp is nothing short of incredible with a few basic bolt-ons and E85, and is likely more than enough power for a vast majority.
BMW S55 Reliability
As previously mentioned, I believe a significant reason the N54 was released in the 335i (and eventually 135i, 535i, 1M, etc) was to work out the early reliability issues. The N54 had its fair share, which BMW committed to fixing through numerous recalls and extended warranties on problematic components. BMW eventually figured out the N54, which is now a relatively reliable engine. The N55 was immediately a more reliable engine from the start. Then finally the S55 was released. So far, there do not seem to be any significant reliability issues or concerns. Given how much I trust the reliability of my N54, and the fact BMW worked out the early issues before releasing a twin-turbo engine in the M3, I believe the S55 will be a very reliable motor for most.
The N54 and S55 are the two best BMW engines for anyone looking for serious horsepower
As emission laws continue to become stricter, I strongly believe turbocharged engines are a brighter potential future of automotive engines, as opposed to electric engines. In order to save automotive enthusiasts from a boring future, there needs to be a company pushing the boundaries of smaller, more efficient turbocharged engines that remain powerful and exciting to drive. In my opinion, BMW is doing just that. The BMW N54 and S55 engines are shining examples of the capabilities of turbocharging. Three liter, inline-six engines pushing 700+whp on mostly stock components is nothing to snarl at. There are many excellent turbo engines in the world right now, however, not many are able to run that kind of power without significant displacement or internal engines modifications. It is my opinion that BMW is currently producing the best turbocharged 6 cylinder engines in the world right now, and the N54 and S55 are the two I would own.