The Audi 21 is a 1,984 cc, inline-four petrol engine produced between 1972 and 1978. It was developed as an evolution of the 1T engine, featuring a larger displacement and improved breathing for enhanced torque output. Equipped with a single overhead camshaft (SOHC) and twin Solex 32 PDSI carburetors in higher-output versions, it delivered up to 85 kW (115 PS) in standard tune. This engine formed part of Audi's transition toward more refined, performance-oriented compact sedans.
Fitted primarily to the Audi 80 (B1) and Audi 100 (C2) models, the 21 engine was engineered to offer a balance of smoothness, responsiveness, and mid-range power. It contributed to Audi's growing reputation for precision engineering during the 1970s. Emissions control remained basic, relying on crankcase ventilation and ignition timing, meeting pre-Euro German TA Luft standards applicable at the time.
One documented concern is intake manifold cracking due to thermal cycling, particularly in models subjected to frequent cold-start/warm-up cycles. This issue, referenced in Audi Technical Service Bulletin 73-06-02, stems from material fatigue in the cast-aluminum manifold. Later production runs incorporated revised casting techniques and improved heat shielding to mitigate cracking risks.
Production years 1972–1978 meet pre-Euro German TA Luft standards; no formal Euro classification applies (VCA UK Type Approval not applicable).
The Audi 21 is a 1,984 cc inline-four petrol engine engineered for compact and mid-size sedans (1972–1978). It combines SOHC valvetrain architecture with dual-carburetor fuel delivery in performance variants to deliver improved torque and drivability. Designed to meet evolving emissions benchmarks in West Germany, it prioritizes mechanical robustness and serviceability over high specific output.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,984 cc | |
| Fuel type | Petrol (Unleaded RON 95) | |
| Configuration | Inline-4, SOHC, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.5 mm | |
| Power output | 66–85 kW (90–115 PS) @ 5,200–5,500 rpm | |
| Torque | 145–160 Nm @ 3,000–3,800 rpm | |
| Fuel system | Single or twin Solex 32 PDSI carburetor | |
| Emissions standard | Pre-Euro (German TA Luft 1969) | |
| Compression ratio | 8.8:1 – 9.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven camshaft | |
| Oil type | SAE 10W-40 mineral oil | |
| Dry weight | 132 kg |
The SOHC dual-carburetor configuration provides enhanced throttle response but requires synchronized adjustment to maintain balance. SAE 10W-40 mineral oil is specified due to camshaft and chain lubrication requirements under sustained load. Cold-weather operation may require choke pre-setting and idle speed adjustment to prevent stalling. The twin Solex setup demands regular cleaning and float-level checks to avoid mixture imbalances. Later model-year engines benefit from revised intake manifolds per Audi SIB 73-06-02, reducing cracking risk. Ignition timing and dwell angle must be manually set during service using factory tools to ensure emissions compliance and fuel efficiency.
Oil Specs: Requires SAE 10W-40 mineral oil (Audi SIB 72-04-05). Synthetic oils not approved due to seal compatibility.
Emissions: Pre-Euro TA Luft 1969 standards apply to all 21 models (VCA Historical Archive Ref. HA/72/002). No Euro classification exists for this era.
Power Ratings: Measured under DIN 70020 standards. Output varies with ambient temperature and fuel quality (Audi TIS Doc. A18150).
Audi Technical Information System (TIS): Docs A17930, A18150, SIB 72-04-05, SIB 73-06-02
VCA Historical Vehicle Records Archive (HA/72/002)
DIN 70020 Engine Power Measurement Standard
The Audi 21 was used across Audi's B1 and C2 platforms with longitudinal mounting and shared architecture with Volkswagen Group components. This engine received platform-specific adaptations-intake manifold revisions for high-load applications-and from 1975 the facelifted Audi 80 LS adopted a twin-carburetor setup, creating interchange limits. Partnerships enabled shared tooling and parts with Volkswagen's EA827 engine family, allowing cross-manufacturer service compatibility. 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 starter motor (Audi TIS A17930). The 5th digit of the VIN indicates engine type ('2' for 21 series). Pre-1974 models have chrome valve covers with ribbed design; post-1974 units use matte-finish covers. Critical differentiation from EA827: Audi 21 uses Solex 32 PDSI carburetor with manual choke, while EA827 variants use Pierburg units. Service parts require model-year verification—intake manifolds before 03/1973 are incompatible with post-1974 models due to routing changes (Audi SIB 73-06-02).
The 21's primary reliability risk is intake manifold cracking under thermal stress, with elevated incidence in stop-start urban use. Internal Audi field reports from 1975 noted increased manifold failures in city-driven B1 platform vehicles, while UK DVSA vintage vehicle records show intake-related faults dominate MOT advisories. Infrequent use and ethanol-blended fuels increase mixture instability, making seasonal maintenance and correct oil usage critical.
Analysis derived from Audi technical bulletins (1972-1978) and UK DVSA vintage vehicle failure statistics (2010-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about AUDI 21.
Comprehensive technical documentation and regulatory references
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AUDI Official Site
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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)
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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
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VCA Certification Portal
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