Forged Piston Set (Factory Specs), Mahle - F8X M2/M3/M4

Mahle Motorsports S55 pistons are forged for strength, light weight, and low drag to be a more specialized application than stock BMW pistons. Factory BMW pistons are cast aluminum, which is fine for the intended power output and durability. But increase the performance, especially on turbocharged engines, and the cast aluminum becomes a weak link at some point. The strength of cast parts is susceptible to heat, detonation/knock, and other timing or fuel issues. These types of combustion forces can make it brittle or even deform the piston shape or size. Forged pistons are inherently a stronger material and more robust in these extreme conditions.

This piston set uses all of the stock specs - no oversize and stock compression - to be used as a replacement piston set better able to cope with added boost.

Full specs -
Bore: 84.0mm
Stroke: 89.6mm
Rod length: 144.35mm
Compression height: 32.4mm
Pin diameter: 22mm
Piston crown volume: -10.5cc
Weight: 325g
Compression ratio: 10.2:1

Mahle uses their high-performance 2618 alloy for these S55 pistons. This is a material usually reserved for racing and other "heavy duty" turbo applications. The 2618 is a low silicon and high expansion material with better tolerances and higher resistance to detonation. These pistons will be softer and more ductile than a piston with more silicon content. This allows the piston to "deform" and better absorb combustion forces before a catastrophic failure. One side effect is these pistons will expand from a smaller diameter when cold, which may result in piston slap knocking noises that should go away when the engine reaches operating temp. The 2618 pistons also feature hard-anodized ring lands that resist wear better than un-protected surfaces.

Mahle Motorsports pistons are better engineered than mass-market OEM pistons. Quality and machining is much more tightly controlled, ensuring superior performance. This piston set has a ceramic-based thermal coating on the piston top (crown) that greatly reduces heat transfer and shock into the alloy. Mahle also uses a Grafal coating on piston skirts that reduces drag, friction, scuffing, and cylinder bore wear and a phosphate coating on the rest of the piston.

All pistons include a ring set, wrist pins, and circlips.

Made in the USA.

BMW Fitments:

2 Series
F87 (2016+) > M2 Competition S55 (2019+)
3 Series
F80 (2015-2018) > M3 (2015-2018)
4 Series
F82 / F83 (2015-2020) > M4 (2015-2020)
F82 / F83 (2015-2020) > M4 GTS