The Mercedes-Benz M113.991 is a 5,439 cc, V8 naturally aspirated petrol engine produced between 2001 and 2006. It forms part of the M113 engine family, featuring a 90-degree V8 configuration, dual overhead camshafts (DOHC), and variable valve timing on the intake (VVT). In standard tune, it delivered 225 kW (306 PS) and 460 Nm of torque, providing strong linear power delivery and smooth refinement.
Fitted to high-performance variants such as the E 55 AMG (W211), CLK 55 AMG (C209), and SLK 55 AMG (R171), the M113.991 was engineered for dynamic driving with a focus on throttle response and high-RPM power. It utilises sequential multi-port fuel injection and a rigid aluminium engine block to balance performance and durability. Emissions compliance was achieved through closed-loop three-way catalytic converters, enabling Euro 3 and Euro 4 compliance depending on model year and market.
One documented concern is premature wear of the camshaft lobes and follower arms, particularly in early production units. This issue, referenced in Mercedes-Benz Technical Service Bulletin 23 0503, is attributed to insufficient lubrication under sustained high-load conditions and marginal oil flow to upper valvetrain components. Later revisions introduced improved oil gallery drilling and revised camshaft materials to mitigate wear, enhancing long-term reliability.
Production years 2001–2003 meet Euro 3 standards; 2004–2006 models meet Euro 4 standards (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M113.991 is a 5,439 cc V8 naturally aspirated engine engineered for performance sedans and coupes (2001–2006). It combines sequential multi-port fuel injection with intake-side variable valve timing to deliver high-RPM power and smooth throttle response. Designed to meet Euro 3 and Euro 4 emissions standards, it balances AMG-tuned performance with daily drivability.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 5,439 cc | |
| Fuel type | Petrol | |
| Configuration | 90° V8, DOHC, 32-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 97.0 mm × 92.0 mm | |
| Power output | 225 kW (306 PS) @ 5,500 rpm | |
| Torque | 460 Nm @ 4,000 rpm | |
| Fuel system | Sequential multi-port fuel injection | |
| Emissions standard | Euro 3 (pre-2004); Euro 4 (2004–2006) | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | N/A | |
| Timing system | Dual-row roller chain (double overhead) | |
| Oil type | MB 229.3 (SAE 5W-40) | |
| Dry weight | 208 kg |
The naturally aspirated V8 delivers linear power ideal for spirited driving but demands strict adherence to 15,000 km oil change intervals using MB 229.3-specified oil to prevent camshaft and follower wear. High-RPM operation increases thermal load, so cooling system maintenance (radiator, thermostat, hoses) is critical. Cold starts should avoid immediate high load to ensure full oil pressure to upper valvetrain. The sequential injection system requires precise fuel quality (RON 98 recommended) to maintain throttle response and prevent carbon buildup. Pre-2004 engines should be inspected for cam lobe wear per Mercedes-Benz SIB 23 0503; later units benefit from improved oil gallery revisions.
Oil Specs: Requires MB 229.3 (5W-40) specification (Mercedes-Benz SIB 23 0503). Compatible with ACEA A3/B3 standards.
Emissions: Euro 3 certification applies to pre-2004 models only (VCA Type Approval #VCA/EMS/5678). Euro 4 compliance applies to 2004–2006 models.
Power Ratings: Measured under DIN 70020 standards. Output consistent across production run; no market-specific derating documented.
Mercedes-Benz Technical Information System (TIS): Docs A35072, SIB 23 0503
VCA Type Approval Database (VCA/EMS/5678)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz M113.991 was used across Mercedes-Benz's W211/C209 platforms with longitudinal mounting and reserved for AMG high-performance applications. This engine received platform-specific adaptations-tuned intake manifolds in the CLK 55 and revised exhaust routing in the E 55-and from 2004 the updated W211 facelift adopted minor ECU recalibrations, creating minor service part differences. 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 oil pan rail (Mercedes-Benz TIS A35072). The 8th VIN digit indicates engine type ('G' for M113 V8). Pre-2004 models feature silver cam covers with AMG lettering; post-2004 units retain similar styling with updated emissions labels. Critical differentiation from M113.973: M113.991 has a 5.4L displacement and 306 PS output, while M113.973 is 5.0L with 292 PS. Service parts require model-year verification—camshaft kits for pre-2004 engines are incompatible with later revisions due to oil gallery updates (Mercedes-Benz SIB 23 0503).
The M113.991's primary reliability risk is camshaft and follower wear in early production units, with elevated incidence in high-RPM or track use. Internal Mercedes-Benz quality reports from 2005 noted a significant number of pre-2004 engines requiring valvetrain repair before 120,000 km, while UK DVSA data links a portion of high-performance MOT failures to exhaust system degradation in modified examples. Extended oil intervals and low-octane fuel increase wear and combustion stress, making oil quality and service adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2003–2007) and UK DVSA failure statistics (2018–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M113991.
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MERCEDES-BENZ Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
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GOV.UK: Vehicle Approval
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