top gear s65 S65 4.2L Street Performance Engine – CarBahn

S65 Engine — Street Performance (4.2L) 

The CarBahn S65 Street Performance engine is engineered to address the known durability limitations of the BMW S65 platform while preserving its high-revving character and naturally aspirated performance. Designed for street and track-day use, this build focuses on improved reliability, sustained high-RPM operation, and long-term durability over the OEM engine. 

OEM Limitations 

The BMW S65 engine is known for several inherent wear points that can compromise reliability over time. Connecting rod bearings and valve springs are common failure items on both S65 and S85 engines, particularly in high-RPM or track-driven applications. Left unaddressed, these components can lead to accelerated wear, valvetrain instability, or catastrophic engine failure. 

CarBahn Engineering Solutions 

The CarBahn S65 engine addresses these weaknesses through targeted internal upgrades and a comprehensive rebuild process. OEM connecting rod bearings are replaced with high-performance CarBahn bearings designed to improve durability under sustained high-RPM operation. CarBahn high-performance valve springs are installed to maintain valvetrain control at elevated engine speeds. 

The engine is upgraded with 2mm oversized 94mm CarBahn-CP forged pistons, increasing displacement while improving strength and thermal stability compared to the factory cast pistons. New head gaskets are installed to ensure proper sealing and long-term reliability. 

Comprehensive Rebuild & Timing Service 

Each engine receives a complete top-end and timing service as part of the rebuild process. This includes a full valve job with new hydraulic lifters, along with new timing chains, timing chain guides, timing chain tensioners, and all associated seals and gaskets. These components are replaced proactively to ensure long-term reliability and consistent performance. 

High-Revving Reliability, Preserved Character 

The CarBahn S65 Street Performance engine retains the naturally aspirated responsiveness and high-RPM character that define the S65 platform, while addressing the known durability shortcomings of the OEM engine. The result is a significantly more reliable and robust engine suitable for spirited street driving and track-day use. 

Proven CarBahn Assembly 

Each CarBahn S65 engine is assembled using the same processes and by the same personnel responsible for CarBahn’s championship-winning race engine programs. With over 46 years of BMW engine-building experience, these engines reflect the same attention to detail and durability that have powered multiple championship-winning efforts, including three prototype racing championships and two overall victories at the 24 Hours of Daytona (2011–2013).