S55 Upgrade Guide: F80 M3, F82 M4 & F87 M2 Competition

The S55 is the twin-turbo 3.0-liter six in the F80 M3, F82/F83 M4 and the F87 M2 Competition and CS. It makes big gains from a tune, but it has a few known weak points, and it gets hot. Sort those out first and it's a strong engine to build on.

M2 owners, check your engine: the 2016–2018 F87 M2 (non-Competition) uses the N55, not the S55. Many parts here don't fit it. The M2 page lists parts for both.

How the S55 makes boost

From the air filter to the exhaust:

1. Intakes: two filters and inlet pipes, one per turbo.
2. Two mono-scroll turbos, each feeding three cylinders.
3. Charge pipes: plastic pipes that carry boost from the turbos up to the cooler.
4. Top-mount charge-air cooler: a water-to-air cooler sitting on top of the engine, cooled by its own low-temperature circuit and a heat exchanger behind the front bumper.
5. J-pipe: the plastic pipe from the cooler down to the throttle body.
6. Downpipes: one per turbo, with the main catalysts, then the mid-pipe and rear exhaust.

Step 1: charge pipes and J-pipe

The factory plastic charge pipes and J-pipe crack, and the J-pipe can fail even at stock boost. Replace them before you tune.

• FTP charge pipe and boost pipe combo: replaces the plastic pipes on the M3 and M4.
• CTS J-pipe: an aluminum replacement for the cooler-to-throttle pipe. Pair it with the CTS charge pipe set.
• VTT cold-side J charge pipe: another aluminum J-pipe.
• MMX charge pipe kit: comes with everything for the install, including the M2 Competition.
• Eventuri carbon charge pipes: carbon pipes that match an Eventuri intake.

Step 2: crank hub

The S55's factory crank hub is a well-known weak point as power goes up. A one-piece hub is cheap insurance on any tuned car.

• 034Motorsport one-piece crank hub with bolt capture plate: a permanent fix for the factory hub.
• MMX one-piece crank hub kit: built for the M2 Competition, M3 and M4.

Step 3: cooling

The S55 heat-soaks quickly. On a hot day or a track day, intake temperatures climb and the car pulls power. Cooling is the upgrade most S55 owners feel the most.

• CSF top-mount charge-air cooler: replaces the cooler on top of the engine. Also offered in a raw finish.
• Mishimoto air-to-water intercooler or the Wagner EVO2 intercooler: other top-mount options.
• CSF front-mount heat exchanger or CTS heat exchanger: more capacity for the cooler circuit. CSF recommends pairing it with an upgraded charge-air cooler.
• Active Autowerke aftercooler cooling kit: an add-on for the charge-air cooling system.
• Oil and DCT: the CSF engine oil cooler and the CSF DCT oil cooler for track cars.

Step 4: tune, intake and downpipes

Tune. This is where most of the S55's extra power comes from.

• Active Autowerke software for the M3 and M4, and the M2 Competition version. Cars built from mid-2020 on have a locked ECU that has to be unlocked first; the listing explains how.
• MMX power control module: a plug-in module that works alongside the factory ECU.

Intakes. An intake adds turbo sound and helps a tuned car breathe.

• CTS intake kit: for the M3, M4 and M2 Competition.
• AWE S-FLO carbon intake: enclosed carbon airboxes for the M3 and M4.
• Eventuri M2 Competition intake: the carbon option for the M2.

Downpipes. Downpipes replace the main catalysts. They help a tuned S55 spool and hold boost, and most need a tune to run properly.

• Catted, for street cars: Active Autowerke with GESI cats (Active Autowerke says these don't need a tune), CTS high-flow cats and Scorpion with high-flow sports cats.
• Catless race downpipes like the Spool race downpipe are for off-road and competition use only.

For sound, a mid-pipe like the Active Autowerke Gen 2 equal-length mid-pipe and a valved rear like the AWE SwitchPath do most of the work. See the exhaust pages linked below for every option.

Step 5: fuel and turbos

Past a tune and bolt-ons, the low-pressure fuel pump is the next limit. Both of these need a tune set up for them.

• Spool S55 fuel pump kit or the PFS drop-in brushless pump.
• Bigger turbos: the VTT S55 GC turbo upgrade for full builds, with a custom tune and the fuel system to match.
• DCT cars at high power: the Spool upgraded DCT clutch set.

Suspension

The F8X cars ride firm from the factory. Coilovers, springs and links let you set the car up for the road or the track.

• Coilovers: KW V3 for the M3 and M4 (M2 version), or Öhlins Road & Track for all three.
• Springs: the Eibach Pro-Kit for the M3 or MMX lowering springs for the M2.
• Sway bars and links: the Dinan adjustable sway bar set and SPL rear toe links, which remove bushing deflection at the rear.

What we'd do

• Daily driver: charge pipes and J-pipe, a crank hub, and a tune. Add springs if you want it lower.
• Weekend or track car: all of the above, plus a charge-air cooler and heat exchanger, catted downpipes, and coilovers.
• Tuned car chasing power: everything above, then a fuel pump, and turbos when you've outgrown the stock pair.

See every part for your car on the F80 M3, F82 M4 and F87 M2 pages, or go straight to M3 intercoolers, M4 exhaust, M3 cooling and M2 suspension.