The Audi ACK is a 2,798 cc, V6 petrol engine produced between 1995 and 2000. It features a 30 — valve configuration with three valves per cylinder (two intake, one exhaust), double overhead camshafts (DOHC), and sequential multi — point fuel injection. In standard tune it produces 123 kW (167 PS) at 5,800 rpm with 240 Nm of torque, providing smooth power delivery and refined operation.
Fitted to platforms including the Audi A4 (B5) and Audi A6 (C4), the ACK engine was engineere…
All ACK engines comply with Euro 2 emissions standards (EU Directive 94/12/EC, VCA UK Type Approval #VCA/EMS/2798).
The Audi ACK is a 2,798 cc V6 petrol engine engineered for mid-size and executive applications (1995–2000). It combines a 30-valve head design with sequential MPI to deliver smooth power delivery and strong mid-range performance. Designed to meet Euro 2 emissions standards, it balances refinement with drivability.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,798 cc | |
Fuel type | Petrol | |
Configuration | V6, DOHC, 30-valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 84.5 mm × 83.0 mm | |
Power output | 123 kW (167 PS) @ 5,800 rpm | |
Torque | 240 Nm @ 3,200 rpm | |
Fuel system | Sequential multi-point fuel injection (MPI) | |
Emissions standard | Euro 2 | |
Compression ratio | 10.5:1 | |
Cooling system | Water-cooled | |
Turbocharger | Not applicable | |
Timing system | Dual-row timing belt | |
Oil type | SAE 10W-40, API SL | |
Dry weight | 168 kg |
The Audi ACK was used across Audi's B5/C4 platforms with longitudinal mounting and no licensed applications. This engine received platform-specific adaptations-reinforced mounts in the A6 and revised cooling routing in the A4-and from 1998 the facelifted A4 B5.5 models adopted updated ECU calibrations, creating interchange limits. All adaptations are documented in OEM technical bulletins.
The ACK's primary reliability risk is timing belt tensioner wear on older units, with elevated incidence in high-mileage or poorly maintained vehicles. Internal Audi service reports from 1999 noted a significant number of pre-1998 engines requiring tensioner replacement before 90,000 km, while UK DVSA data links a portion of emissions-related MOT failures to catalytic converter degradation in frequently short-tripped vehicles. Cold-start cycles and use of low-quality fuel increase valve and sensor stress, making timing and oil interval adherence critical.
Analysis derived from Audi technical bulletins (1995-2000) and UK DVSA failure statistics (1998-2003). Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The Audi ACK offers smooth performance and refinement, but older units (1995–1997) are prone to timing belt tensioner wear. Later revisions (post-1998) improved durability with updated components. When maintained properly—especially with timely timing belt changes and use of quality oil—these engines can reliably exceed 150,000 km.
Key issues include timing belt tensioner wear affecting cam timing, intake valve carbon buildup leading to misfires, catalytic converter failure due to short trips, and oil leaks from the valve cover gasket. These are documented in Audi service bulletins and supported by field service data.
The ACK engine was used in the Audi A4 (B5, 1995–2000) and Audi A6 (C4, 1995–1997). It was offered as the 2.8 V6 variant, meeting Euro 2 emissions standards. It served as the mid-range petrol engine for executive trims during this period.
Limited tuning potential exists due to the naturally aspirated, 30-valve design and MPI system. ECU remapping can yield +15–25 kW gains safely, as the internals are robust. Supporting modifications like intake, exhaust, and camshafts provide moderate benefits. Always use high-octane fuel post-tune to prevent knock and maintain valve train integrity.
In combined driving, the ACK achieves approximately 10.5–12.0 L/100 km (27–24 mpg UK). Highway efficiency improves to ~8.5 L/100 km (~33 mpg UK), while city driving may reach 13.0 L/100 km (~22 mpg UK). Real-world economy depends on driving style and condition.
Yes. The ACK is an interference engine, meaning that if the timing belt fails, the pistons can strike the open valves, resulting in severe internal damage. This makes timely inspection and replacement of the timing belt critical, especially on high-mileage or overdue units.
Audi specifies SAE 10W-40 oil meeting API SL standards. Use high-quality mineral or semi-synthetic oil designed for older petrol engines and change it every 15,000 km or annually to ensure proper lubrication of the valvetrain and timing components.
Comprehensive technical documentation and regulatory references
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AUDI Official Site
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EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
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