With over 40 years of history, BMW’s M badge has long represented the pinnacle of performance in the consumer motorsport world. Ever since the first M1 debuted, these cars have dominated roads and race tracks all over the world.
Debuting under the hood of the BMW M3 and BMW M4 in 2014, the S55 engine is next in line from this prestigious motorsport group.
Returning to their legendary inline-six design, the S55 represents a move to downsize from the V-8s under the hood of the last generation of M cars.
How does the S55 stack up compared to previous offerings? Read on to learn all about it.
In the past, the engines powering many of BMW’s M cars were naturally-aspirated. The M series has always maintained a devoted following of enthusiasts who take great pride in their cars and the engines that power them.
So, when the brand announced that a turbo would be coming to the M series, enthusiasts were a bit concerned, but a turbo-charged M car represents BMW embracing modern design elements. It’s a shift toward smaller form factors, improved fuel economy, and lower emissions with the BMW performance parts you’ve grown to trust.
The S55 isn’t BMW’s first I6 offering to feature a turbocharger. That distinction belongs to the N55 engine that first appeared mated to the F07 5-series Gran Turismo.
The 3.0 L N55 went on to receive numerous accolades. It appeared on Ward’s Top Ten Engines list for three years in a row and was voted 2014’s Engine of the Year in the 2.5-3.0 L category.
N55 and S55
After receiving such praise for their work with turbochargers and seeing the automotive landscape shift to smaller engines, it made sense to continue the trend.
The S55 engine builds on the foundation laid by the N55. They both feature the same 84 mm bore, 86.9 mm stroke, and 2,729 cc displacement.
However, the S55 packs a punch the N55 can’t match. Unlike the N55’s single turbo with twin-power technology, the S55 features two classic turbochargers.
The differences don’t stop there. The S55 also features Valvetronic technology to improve throttle response, decrease fuel consumption, and lower CO2 emissions. It’s an engine designed with an eye toward modern concerns.
Other improvements include more advanced intercoolers to chill the engine, twin fuel pumps, stronger pistons, a high-performance lightweight crankshaft, and a closed-deck engine bay.
Aside from the turbos, the closed-deck design is perhaps the biggest improvement over the N55. It allows for improved power output thanks to higher cylinder pressure.
Thanks to the twin-turbo configuration, the S55 has an incredibly even torque output. While this is true of most turbo-charged cars, the S55 allows you to tap into wheel-spinning torque from as low as 1850 RPM, and delivers it linearly all the way to 5500 RPM.
BMW’s Valvetronic and Double-Vanos technology is the reason that torque delivery is so consistent across the rev-band.
5500 RPM to 7300 RPM is the engine’s optimal performance band, with its top speed reachable at 7600 RPM. This engine is capable of providing both consistent torque application and an incredible rate of speed.
In its stock configuration, the S55 engine makes 425 HP and 406 lb-ft of torque. While these numbers are certainly impressive, it’s capable of so much more with a few upgrades.
The S55 engine also holds the record for the most powerful BMW engine ever made. BMW tuning brought a heavily-modified version up to 1,150 HP at the wheels.
This engine’s twin turbos each produce up to 18 pounds of boost to the cylinders and come with an electronic wastegate. Thanks to this design, the engine doesn’t need a blow-off valve.
To ensure oil distribution even under tight cornering, the S55 also boasts a secondary oil pump. This pump pushes oil from the sides of the pan into the engine.
Where To Find the S55
The S55 is a highly-capable engine. It found a home under the hood of a number of production models and performance cars.
In its stock form, it powers the F80 M3, the F82 M4, and the F83 M4.
A slightly detuned version powers the F87 M2 CS Racing. Here, it makes between 275 and 360 HP.
Other applications in the M2 include the F87 M2 Competition, where the engine produces 405 HP, and the F87 M2 CS racing with 444 HP.
On high-performance M3s, the S55 can be found powering the F80 M3 Competition making 444 HP and the F80 M3 CS Racing with 453 HP.
Its M4 performance applications include the F82 and F83 M4 Competition with 444 HP, the F83 M4 CS Racing with 453 HP, the F82 M4 GTS, and F83 M4 GTM Champion Edition. The latter two both feature 493 HP thanks to a water injection system.
Is the S55 Reliable?
As the years pass by, the S55 continues to prove to be a fairly reliable engine. Like all BMW engines, it does occasionally experience issues like high-pressure fuel pump failure and carbon build-up, but those problems are relatively rare.
The only major issue that allegedly affected a few of these engines was a spun crank hub. Because it borrowed the crank hub design from the N54 and N55 engines, some claimed early editions of the N55 engine experienced crank hub problems.
However, BMW improved the design of the crank hub in 2016, which seemed to put an end to the issue. It turned out that TPG Tuning, an aftermarket parts manufacturer, had wildly exaggerated claims in an effort to sell more of their products.
Aside from the crank hub scare, the S55 has no major issues to report. Many of these engines are still going strong more than eight years from their initial production date.
The S55 Powers the BMW M3 and BMW M4
BMW’s S55 engine is an incredible power plant. It brought turbo capabilities to the M series when it first appeared in 2014 with the BMW M3 and BMW M4.
It’s an improvement of the award-winning N55 engine, and it features twin turbochargers and a host of other upgrades.
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