BMW Gives the S58 a Second Spark Plug per Cylinder, and US Cars Aren't Getting It Yet

Starting this month, every S58 inline-six that BMW M builds for the M3 and M4 has two spark plugs in each cylinder. One sits where it always has. The other fires inside a tiny chamber of its own, tucked into the cylinder head, and it only takes charge when the engine is working hard. BMW calls the system M Ignite, and it is the most significant technical update the S58 has received, as BMWBlog put it.

The catch for American buyers: BMW told BMWBlog that US-market G8x cars currently in production will not get it, and it would not say when that changes. For now, the newest version of BMW M's six is a European story, built to pass emissions rules that do not exist here.

What a pre-chamber actually does

In a normal gasoline engine, one spark plug lights the mixture at one point and the flame front spreads outward from there. That works, but it is slow at the edges of the chamber, and slow, uneven burning is where knock starts. Pre-chamber ignition attacks that problem by lighting the charge from many points at once.

According to BMW's announcement, the pre-chamber is positioned within the cylinder head and connected to the main combustion chamber by overflow openings. It has its own spark plug and its own ignition coil, so the engine effectively carries two ignition systems. Part of the fuel and air mixture is pushed through those openings into the pre-chamber and ignited there.

The flames that result leave the pre-chamber at around the speed of sound, BMW says, and those jets ignite the mixture above the piston at multiple points at the same time. The payoff is a much higher combustion speed. BMW lists three effects: knock is countered effectively, exhaust gas temperature drops, and fuel consumption under high load falls substantially.

Two plugs, two jobs

The clever part is that M Ignite does not run the pre-chamber all the time. BMW says that at low and medium revs the conventional plug in the main chamber fires before the pre-chamber plug, so around town the S58 lights its fuel the old way. When revs and load climb, the pre-chamber takes over the lead role.

That split matters because pre-chamber systems are at their best at high load, where the faster burn lets an engine run more aggressive timing or more compression without detonation. BMW pairs M Ignite with a higher compression ratio and with turbochargers that use variable turbine geometry, a first for this engine according to BMWBlog. BMWBlog also reports revised exhaust ports, camshafts and pistons. BMW has not published the new compression ratio or turbo specifications.

Built for Euro 7, sold as a track-day upgrade

BMW is upfront that regulation is half the reason. The new European Euro 7 standard comes into force in November 2026, and BMW says M Ignite plays a major role in meeting it, so cars fitted with the technology will keep meeting European registration requirements.

The other half is the part enthusiasts will feel. BMW says the efficiency gains are biggest when the engine is pushed to its limits, and it points straight at track days: lower fuel consumption under high load means M customers can keep lapping for longer on the same amount of fuel. Anyone who has watched a fuel gauge fall through a 20-minute session in an M4 knows that is not a small thing.

Power stays put. BMW says displacement and output for every model with M Ignite will be unchanged from the corresponding outgoing engines. BMWBlog quoted BMW M as saying the sound becomes even more throaty at higher revs, which is about as close to a performance promise as this update gets.

Not a new idea, but a new execution

Pre-chamber combustion has been around for decades. BMWBlog notes that Honda used a version of it in the 1970s Civic and that Maserati uses it today in its Nettuno V6. BMW's take is its own design, patented in 2024, and the company frames it as technology transferred from motorsport to a production engine.

What is new is putting it into a high-volume, high-output turbo six that people also tune. The S58 has been one of the most modified Euro engines on the street since it arrived, and the hardware changes here, from the pre-chamber to the VTG turbos and new pistons, mean tuners will be learning a different engine rather than a tweaked calibration.

Why the US misses out

BMWBlog asked BMW directly. "G8x vehicles currently in production will not receive the Ignite technology in the US," BMW said in a statement to the outlet, adding: "We will not speculate on when it may arrive in the US or in which model(s)."

BMWBlog's read is that the US has no regulation equivalent to Euro 7, which is why American cars are not in line for the update right now. The US-only M3 CS manual, sold as the Handschalter, also misses out, according to the outlet. That leaves two versions of the S58 on sale at the same time depending on where a car is built to be sold.

For US owners, nothing about their engines got worse this month. But the M3 and M4 that European buyers take to the Nordschleife from July onward will burn less fuel per lap than the same car in Georgia or California, and BMW has not said whether that ever changes in this generation.