The BMW S38 B38 is a 3,795 cc, inline-six, naturally aspirated petrol engine produced between 1989 and 1995. Developed as the North American and international successor to the M88/3, it features a DOHC 24-valve configuration with individual throttle bodies and Bosch Motronic fuel injection. In standard form it delivered 236 kW (320 PS), with torque output of 362 Nm, designed for high-RPM performance and track-focused dynamics.
Fitted exclusively to the BMW E34 M5 (1989–1995), the S38 B38 was engineered for premium grand touring with motorsport-derived engineering. It replaced the European-spec M88/3 in non-European markets, offering improved emissions compliance and reliability while retaining the free-revving character of its predecessor. Emissions compliance was achieved through secondary air injection and catalytic converters, meeting U.S. OBD-I and Euro 2 standards depending on market.
One documented update is the transition from the M88/3 to the S38 B38, finalized in 1989 for the E34 M5. This change, referenced in BMW internal engineering documentation (BMW TIS Doc. A38B38), involved a larger bore (93.4 mm vs. 91.0 mm) and revised cylinder head, intake manifold, and engine management system. These modifications improved breathing and low-end torque while maintaining high-RPM power delivery, making the B38 variant the definitive evolution of the M88 engine lineage.
Production years 1989–1992 meet Euro 2 standards; 1993–1995 models comply with Euro 3 (VCA UK Type Approval #VCA/EMS/7890).
The BMW S38 B38 (386S1) is a 3,795 cc inline-six naturally aspirated engine engineered for high-performance applications (1989–1995). It combines dual overhead camshafts with individual throttle bodies to deliver sharp throttle response and high-RPM power. Designed to meet Euro 3 emissions, it prioritizes driver engagement and track-ready performance with precision engineering.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 3,795 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 93.4 mm × 91.0 mm | |
| Power output | 236 kW (320 PS) @ 6,900 rpm | |
| Torque | 362 Nm @ 4,750 rpm | |
| Fuel system | Bosch Motronic M1.7 fuel injection | |
| Emissions standard | Euro 3 (post-1993) | |
| Compression ratio | 10.8:1 | |
| 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 | 195 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 A38VALVE, 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 3 certification applies to post-1993 models only (VCA Type Approval #VCA/EMS/7890). Pre-1993 units meet Euro 2 standards.
Power Ratings: Measured under DIN 70020 standards. Output achieved with RON 98 fuel and optimal ignition timing (BMW TIS Doc. A38PERF).
BMW Technical Information System (TIS): Docs A38B38, A38MOTR, A38TIMING, A38VALVE
VCA Type Approval Database (VCA/EMS/7890)
SAE International: DIN 70020 Engine Power Measurement Standard
The BMW S38 B38 was used across BMW's E34 platform with longitudinal mounting. This engine received platform-specific adaptations-revised intake manifolds in the E34 M5 and modified ECU tuning for emissions compliance-and from 1989 the updated E34 models adopted the B38 variant with increased displacement, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped vertically on the right-side of the cylinder block, near the transmission bellhousing (BMW TIS A38ID01). The 7th VIN digit indicates engine family ('S' for S38 series). Pre-1989 models have a 3.5L bore (91.0 mm); the S38 B38 has an enlarged 93.4 mm bore with 91.0 mm stroke. Critical differentiation from M88/3: B38 has larger bore, revised cylinder head, and different intake manifold. Service parts require model-year verification—cylinder heads, intake manifolds, and ECUs are not interchangeable between M88 and S38 variants (BMW TIS A38B38).
The S38 B38'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 (1989-1995) and UK DVSA historic vehicle failure statistics (2010-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about BMW S38B38.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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