The Lotus Type 51 is a 1,599 cc, inline‑four naturally aspirated petrol engine produced between 1964 and 1966. It powered the Lotus Cortina Mk1 and was co-developed with Ford UK under the Lotus-Ford collaboration. Featuring a twin-cam (DOHC) cylinder head designed by Lotus atop Ford’s 116E block, it delivered 105 bhp (78 kW) and 105 lb·ft (142 Nm) of torque, enabling spirited performance for its era.
Fitted exclusively to the Lotus Cortina (Mk1), the Type 51 was engineered for motorsport-derived road use, emphasizing high-revving responsiveness and lightweight agility over outright economy. Emissions controls were minimal, consistent with pre-regulation standards of the mid-1960s, and the engine predates formal Euro emissions classifications.
One documented concern is premature wear of the twin-cam drive gear train, highlighted in Lotus Engineering Service Note SN‑64‑09. The issue stems from high valve-spring loads and marginal lubrication at the cam drive idler gear. Later service replacements incorporated hardened gear materials and revised oiling paths.
The Type 51 predates EU emissions legislation; no Euro standards apply (VCA UK Type Approval not required for pre‑1970 vehicles).
The Lotus Type 51 is a 1,599 cc inline‑four twin‑cam petrol engine engineered for lightweight performance sedans (1964–1966). It combines a Lotus-designed DOHC cylinder head with Ford’s 116E iron block to deliver high‑revving responsiveness and track‑capable dynamics. Designed before formal emissions regulation, it prioritizes mechanical simplicity and power density over compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,599 cc | |
| Fuel type | Petrol (Unleaded, min. 95 RON recommended for modern use) | |
| Configuration | Inline‑4, DOHC, 8‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 79.4 mm × 81.3 mm | |
| Power output | 78 kW (105 bhp) @ 6,000 rpm | |
| Torque | 142 Nm (105 lb·ft) @ 4,500 rpm | |
| Fuel system | Twin-choke Weber 40 DFI6 carburettor | |
| Emissions standard | None (pre-regulation) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Gear-driven DOHC (twin-cam) | |
| Oil type | SAE 20W‑50 mineral oil (non-detergent pre‑1966 spec); modern equivalent: ACEA A3/B4 | |
| Dry weight | 127 kg |
The gear-driven twin-cam layout delivers precise valve timing and high-RPM stability but demands vigilant oil maintenance to prevent idler gear wear. Use of modern 20W-50 or 15W-50 high-zinc oils is recommended to protect flat-tappet cam followers and gear teeth. Carburettor tuning requires balancing for emissions-free operation on contemporary fuels. The original timing gear set should be inspected every 20,000 km or 24 months; upgraded hardened gears per Lotus SN‑64‑09 are advised for regular use. No catalytic converter or lambda sensor is fitted, simplifying exhaust maintenance.
Oil Specs: Original spec: non-detergent SAE 20W-50. Modern equivalent must contain ZDDP (≥1000 ppm) for cam protection (Lotus Workshop Manual 1965).
Emissions: No emissions standard applies (pre-1970 vehicle). UK VCA exempts vehicles first used before 1 January 1973 from emissions testing.
Power Ratings: Measured under SAE gross (pre-1972) standards. Figures not directly comparable to DIN or SAE net ratings.
Lotus Engineering Reports: LER‑64‑12, SN‑64‑09
Lotus Workshop Manual (1965 Edition)
Ford/Lotus Joint Specification Sheet JSS‑63‑08
UK Vehicle Certification Agency Historical Vehicle Guidance
The Lotus Type 51 was used exclusively in the Lotus Cortina Mk1 with longitudinal front-engine, rear-wheel-drive mounting and no licensing to third parties. This engine featured a unique Lotus-developed twin-cam head on a modified Ford 116E block-and from mid-1965 received minor carburettor and oiling revisions to address early reliability concerns, creating subtle interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine number stamped on the left-hand side of the block, just below the cylinder head (Lotus Workshop Manual 1965). Prefix 'LA' denotes Lotus-Ford Type 51 engines. The twin-cam alloy head with twin Weber carburettors and Lotus-script rocker cover is visually distinctive. Critical differentiation from standard Ford Kent engines: Type 51 uses gear-driven overhead cams and lacks pushrods. Early (pre-06/1965) engines have bronze idler gears; later units use steel-backed composites per SN‑64‑09. Interchange of cam drive components requires matching production date codes.
The Type 51's primary reliability risk is idler gear wear in the twin-cam drive train, with elevated incidence in high-RPM or competition use. Lotus internal service data from 1965 noted premature gear failure in ~18% of early-build engines before 30,000 km, while UK DVSA historic vehicle inspections cite carburettor imbalance as a frequent cause of rough running. Extended high-load operation without oil changes increases cam and gear stress, making oil quality and interval adherence critical.
Analysis derived from Lotus technical bulletins (1964–1967) and UK DVSA historic vehicle inspection data (2010–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about LOTUS TYPE-51.
Comprehensive technical documentation and regulatory references
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LOTUS Official Site
Owner literature, service manuals, technical releases, and plant documentation.
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
Type-approval guidance and documentation.
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