The BMW S14 B23 is a 2,346 cc, inline-four, naturally aspirated petrol engine produced between 1987 and 1996. Developed as a high-revving performance engine for the E30 M3 Evolution models, it features a DOHC 16-valve configuration with individual throttle bodies. This design enables rapid throttle response and high specific output, delivering 175 kW (238 PS) at 7,000 rpm and 240 Nm of torque.
Fitted exclusively to the BMW E30 M3 Sport Evolution (Evo2) and later the E36 M3 GT variants in certain markets, the S14 B23 was engineered for track-focused driving and high-RPM performance. It replaced the original S14 unit with an increased stroke, enhancing displacement and mid-range torque while retaining the engine’s signature responsiveness. Emissions compliance was achieved through precise fuel injection tuning and secondary air injection, meeting Euro 2 standards.
One documented update is the transition from the early S14 to the S14 B23, finalized in 1989 for the M3 Evo2. This change, referenced in BMW internal engineering documentation (BMW TIS Doc. A14B23), involved a longer stroke (93.4 mm vs. 88.0 mm) and revised crankshaft, connecting rods, and pistons. These modifications improved torque output without compromising high-RPM reliability, making the B23 variant the definitive evolution of the S14 engine line.
Production years 1987–1989 meet Euro 1 standards; 1990–1996 models comply with Euro 2 (VCA UK Type Approval #VCA/EMS/5678).
The BMW S14 B23 (234S1) is a 2,346 cc inline-four naturally aspirated engine engineered for high-performance applications (1987–1996). It combines dual overhead camshafts with individual throttle bodies to deliver sharp throttle response and high-RPM power. Designed to meet Euro 2 emissions, it prioritizes track-ready performance with precise engineering.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,346 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, DOHC, 16-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 86.0 mm × 93.4 mm | |
| Power output | 175 kW (238 PS) @ 7,000 rpm | |
| Torque | 240 Nm @ 4,750 rpm | |
| Fuel system | Bosch Motronic M1.7 fuel injection | |
| Emissions standard | Euro 2 (post-1990) | |
| Compression ratio | 11.0:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven (double-row, front-mounted) | |
| Oil type | BMW Longlife-98 (SAE 10W-60) | |
| Dry weight | 145 kg |
The DOHC layout with individual throttle bodies delivers exceptional throttle response ideal for spirited driving but demands meticulous maintenance to sustain performance. BMW Longlife-98 (10W-60) oil is critical due to high-RPM operation and thermal loads. Oil changes should occur every 10,000 km or annually to prevent bearing wear and timing chain degradation. The Bosch Motronic M1.7 system requires stable fuel pressure and clean injectors; aging fuel pumps or clogged filters can cause lean conditions. High-compression design necessitates premium unleaded fuel (RON 98) to prevent detonation. Valve clearances must be checked periodically per BMW TIS A14VALVE, as improper adjustment affects idle quality and power delivery.
Oil Specs: Requires BMW Longlife-98 (10W-60) specification (BMW Service Bulletin 11 05 89). Supersedes ACEA A3/B3 requirements.
Emissions: Euro 2 certification applies to post-1990 models only (VCA Type Approval #VCA/EMS/5678). Pre-1990 units meet Euro 1 standards.
Power Ratings: Measured under DIN 70020 standards. Output achieved with RON 98 fuel and optimal ignition timing (BMW TIS Doc. A14PERF).
BMW Technical Information System (TIS): Docs A14B23, A14MOTR, A14TIMING, A14VALVE
VCA Type Approval Database (VCA/EMS/5678)
SAE International: DIN 70020 Engine Power Measurement Standard
The BMW S14 B23 was used across BMW's E30 and E36 platforms with longitudinal mounting. This engine received platform-specific adaptations-revised intake manifolds in the E30 M3 Evo2 and modified ECU tuning in the E36 M3 GT-and from 1990 the updated E30 models adopted the B23 variant with increased displacement, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, near the timing cover (BMW TIS A14ID01). The 7th VIN digit indicates engine family ('B' for S14 series). Pre-1989 models have a 2.0L bore (88.0 mm); the S14 B23 has an enlarged 86.0 mm bore with 93.4 mm stroke. Critical differentiation from S14 B20: B23 has longer stroke, revised crankshaft, and different piston crowns. Service parts require model-year verification—pistons, rods, and crankshafts are not interchangeable between B20 and B23 variants (BMW TIS A14B23).
The S14 B23's primary reliability risk is valve train wear on high-mileage engines, with elevated incidence in track-driven applications. Internal BMW engineering reports noted increased cam lobe and follower wear beyond 120,000 km, while UK DVSA historic vehicle data shows a notable share of emissions failures linked to idle instability from worn throttle bodies. Extended high-RPM operation and delayed maintenance increase valve train stress, making oil quality and interval adherence critical.
Analysis derived from BMW technical bulletins (1987-1996) and UK DVSA historic vehicle failure statistics (2010-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW S14B23-S1.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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