The ZRP crankshaft for the BMW M3 S14B25 2.5 L is designed for engine builds that maintain a stroke of 87 mm. It can also be used on the S14B23 in a stroker configuration to increase stroke and cubic capacity with appropriate connecting rods and pistons.
Part number C-BMW-002 is fully CNC-machined from solid 4340 aerospace-grade steel. Its Aero-Wing-profiled counterweights reduce losses caused by air and oil mixing in the crankcase. Direct oil ducts supply the crankshaft journals, while the connection spokes of the bearing surfaces are engineered to better distribute mechanical stresses.
Technical Specifications
- Brand: ZRP
- Manufacturer Part Number: C-BMW-002
- Primary Application: BMW M3 2.5 L, S14B25 engine
- Additional application: BMW M3 S14B23 (in preparation for stroker conversion)
- Configuration for S14B25: standard stroke
- Manufacturing: CNC machined from solid stock
- Material: 4340 billet steel, aerospace grade
- Stroke: 87.00 mm
- Journal diameter: 54.99 mm
- Rod journal diameter: 47.991 mm
- Weight: 20.50 kg
- Balancing: performed on Sunnen equipment, with inspection report provided
Design and oiling
- Aero-Wing counterweights: profile designed to minimize drops due to oil churning in the crankcase.
- Direct oil ducts: designed to optimize crankshaft oiling.
- Chamfered oil holes: finish on the inlets of the oiling lines.
- Connection spoke radii of bearing surfaces: stress distribution in transition zones.
- Lightweight crankshaft journals with a conical profile: a design that contributes to weight reduction.
Manufacturing Processes and Inspections
- Full CNC machining: precise production of geometries and bearing surfaces.
- Plasma ion nitriding: surface hardening of treated areas.
- Multi-stage heat treatments: achieving the desired mechanical properties.
- Shot blasting: mechanical surface treatment.
- Magnetic particle inspection on each part: detection of surface or near-surface defects.
- Heat treatment to improve abrasion resistance.
- Micro-polishing of bearing surfaces: a finish designed to extend the service life of the bearings.
- Ultrasonic and X-ray inspections: verification of material integrity.
Mounting on the S14B25 and preparation for the S14B23 Stroker
On the S14B25, this part retains the 87 mm stroke. On the S14B23, its use in a Stroker configuration requires a properly matched set of connecting rods and pistons. The final cubic capacity depends on the selected bore: the crankshaft mounting alone is not sufficient to guarantee a cubic capacity of 2.5 liters.
Before assembly, check the bearing clearances, the piston position at top dead center, the compression ratio, and the clearances of the moving parts.
Key Features
- 87 mm stroke suitable for the S14B25 and S14B23 stroker builds.
- Machined from solid 4340 steel.
- Aero-Wing counterweight to minimize mixing drops.
- Direct oil ducts for crankshaft journal oiling.
- Plasma nitriding and micro-polished bearing surfaces.
- Controlled balancing with a balance report provided.
