Forged Oversize Piston Set (1st Over), Mahle - E46 M3, MZ3 S54, Z4M

Mahle Motorsports S54 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 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 set is the stock compression but is a first oversize when the cylinders need to be machined. BMW has a 87.20mm piston set and this is 87.25mm

Full specs -
Bore: 87.25mm
Stroke: 91.0mm
Rod length: 139.0mm
Compression height: 32.3mm
Pin diameter: 21mm
Piston crown volume: -13.1cc
Weight: 340g
Compression ratio: 11.5:1

Mahle uses their high-performance 2618 alloy for their S54 pistons. This is a material usually reserved for racing and other "heavy duty" 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.

Mahle Motorsports pistons are better engineered than mass-market OEM pistons. Quality and machining is much more tightly controlled, ensuring superior performance. Mahle uses a Grafal coating on piston skirts that reduces drag, friction, scuffing, and cylinder bore wear and a phosphate coating on other surfaces.

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

Made in the USA.

BMW Fitments:

3 Series
E46 (99-05) > M3
Z Series
E36/7 / E36/8 Z3 (96-02) > Z3 M - S54
Z Series
E85 / E86 Z4 (03-08) > Z4 M