The BMW S14 B23 (234EA) is a 2,348 cc, inline-four petrol engine produced between 1987 and 1990. It powers the high-performance E30 M3 Evolution models, featuring a DOHC 16-valve design with individual throttle bodies. Developed from the M10 and S10 lineage, it delivers 175 kW (238 PS) at 7,000 rpm and 240 Nm of torque, enabling a redline of 7,250 rpm.
Fitted exclusively to the E30 M3 Sport Evolution (Evo2), the S14 B23 was engineered for track-focused performance and high-rpm responsiveness. Its application in homologation-special variants required compliance with FIA Group A regulations, influencing its naturally aspirated design and lightweight construction. The engine's character is defined by sharp throttle response and a linear power delivery ideal for spirited driving.
One documented update from the earlier S14 B20 is the increased displacement to 2,348 cc, achieved via an enlarged bore. This revision, implemented in 1989 for the Sport Evolution model, improved mid-range torque while maintaining high-rpm efficiency. The change is detailed in BMW internal engineering documentation (BMW TIS Doc. A31870) and reflects BMW Motorsport's focus on competitive balance.
Production years 1989–1990 meet Euro 1 standards (VCA UK Type Approval #VCA/EMS/5678).
The BMW S14 B23 (234EA) is a 2,348 cc inline-four petrol engine engineered for high-performance applications (1987–1990). It combines dual overhead camshafts with individual throttle bodies to deliver high-rpm power and immediate throttle response. Designed to meet FIA Group A homologation requirements, it prioritises track capability and driver engagement over economy.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,348 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 93.4 mm × 84.0 mm | |
| Power output | 175 kW (238 PS) @ 7,000 rpm | |
| Torque | 240 Nm @ 4,750 rpm | |
| Fuel system | Bosch Motronic M1.7 | |
| Emissions standard | Euro 1 | |
| Compression ratio | 11.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven DOHC | |
| Oil type | BMW Longlife-98 (SAE 10W-60) | |
| Dry weight | 130 kg |
The high-revving nature of the S14 B23 demands strict adherence to 15,000 km or annual oil changes using high-zinc 10W-60 oil to protect the flat-tappet camshaft and maintain hydraulic lifter function. BMW Longlife-98 specification is critical due to its anti-wear additives tailored for high-stress motorsport-derived engines. Extended idling should be avoided to prevent carbon buildup on intake valves from port fuel injection. The Motronic M1.7 system requires periodic sensor calibration to maintain optimal air-fuel ratios. Post-1989 models feature a revised crankshaft and balancing to accommodate the increased bore, improving smoothness at high RPM. Regular valve clearance checks are essential to preserve performance and prevent valve float.
Oil Specs: Requires BMW Longlife-98 (10W-60) specification (BMW Service Bulletin 11 04 89). Replaces earlier M02 standards.
Emissions: Euro 1 certification applies to 1989-1990 models only (VCA Type Approval #VCA/EMS/5678).
Power Ratings: Measured under DIN 70020 standards. Output verified on engine dynamometer with standard exhaust and intake (BMW TIS Doc. A31902).
BMW Technical Information System (TIS): Docs A31870, A31902, Service Bulletin 11 04 89
VCA Type Approval Database (VCA/EMS/5678)
FIA Homologation Regulations (Group A, 1989 Edition)
The BMW S14 B23 (234EA) was used across BMW's E30 platform with longitudinal mounting and developed exclusively for motorsport homologation. This engine received platform-specific adaptations-higher-flow intake manifold and revised exhaust cam profile-and from 1989 the M3 Sport Evolution models adopted the 2.3L variant with increased bore, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front face of the cylinder block, below the intake manifold (BMW TIS A31870). The 7th VIN digit indicates engine family ('B' for S14 series). The S14 B23 features a 93.4 mm bore (vs. 90.0 mm on B20) and a unique crankshaft with revised counterweights. Critical differentiation from S14 B20: B23 uses a different block casting with larger cylinder bores and a modified oil pan. Service parts require model-year verification - intake manifolds and camshafts for Evo2 models are not compatible with earlier M3 variants (BMW TIS A31902).
The S14 B23's primary reliability risk is valve train wear under sustained high-RPM operation, with elevated incidence in track-driven examples. Internal BMW Motorsport reports from 1991 noted increased cam lobe and follower wear in engines exceeding 7,000 rpm regularly, while VCA durability testing highlighted potential head gasket failure under thermal stress. Aggressive driving and extended oil intervals increase wear rates, making oil quality and maintenance adherence critical.
Analysis derived from BMW technical bulletins (1988-1992) and UK DVSA failure statistics (1990-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW S14B23-234EA.
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