The 1966 season brought sweeping regulatory changes to Formula One, doubling the permitted engine displacement to three litres. Lotus had previously collaborated with Cosworth to develop the DFV engine, but that unit would not be ready until 1967. In the interim, Colin Chapman struck a deal to use the BRM P75 H16 engine, a technically ambitious sixteen-cylinder unit that promised considerable power on paper.
Chapman drew partial inspiration from the Lotus 38 Indianapolis car, designed by Len Terry, leveraging the team's experience with larger-capacity engines and the suspension demands that came with them. The 43 chassis also introduced the concept of using the engine itself as a structural load-bearing member, with rear suspension attached directly to the engine block — an engineering principle that would be refined and carried forward into the far more successful Lotus 49.
The H16's shortcomings became apparent almost immediately. When the engine arrived at Team Lotus's factory in Hethel, Norfolk, it required four men to lift it from the truck. It proved overweight, mechanically fragile, and incapable of delivering the power its specifications had promised.
The Lotus 43 was scheduled to debut at the 1966 Monaco Grand Prix in the hands of Peter Arundell, but the car was not ready in time. Its first competitive appearance came at the Belgian Grand Prix, where it retired during practice when the engine failed.
The car reappeared at the Italian Grand Prix at Monza but was sidelined again by gearbox failure. Jim Clark then drove the 43 to victory at the United States Grand Prix at Watkins Glen — the only win ever recorded by a car powered by the BRM P75 H16 engine. Clark used a spare engine loaned by the BRM works team for the occasion. The season ended on another low note at the Mexican Grand Prix, where the 43 retired once again with gearbox failure.
The Lotus 43 made its final World Championship appearance at the 1967 South African Grand Prix at Kyalami, with both Jim Clark and new team-mate Graham Hill entered. Neither driver was able to finish the race.
Only two Lotus 43 chassis were ever built. Following their retirement from Formula One competition, both cars were sold to private owners Robert Lamplough and Jock Russell, who fitted them with 4.7-litre Ford V8 engines and ran them in Formula 5000 events.
The Lotus 43 occupies a curious place in Formula One history — a car whose chassis was considered innovative and technically sound, but whose competitive record was crippled by an engine that never delivered on its promise. The structural concepts pioneered in the 43, particularly the use of the engine as a stressed chassis member, were directly inherited by the Lotus 49 and became a cornerstone of subsequent Formula One design philosophy for decades. In that sense, the 43 served as a necessary stepping stone, even if its own results were largely forgettable.
The car also holds a niche place in sim racing history: a driveable reconstruction of the Lotus 43 appeared in 2007 in the freely available "66 Mod" for the PC racing simulation Grand Prix Legends.