The Lotus-Ford Twin Cam is a 1558 cc engine developed for the 1962 Lotus Elan and also used in a variety of other vehicles up until mid 1970s.
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Lotus required a low cost, compact, yet powerful engine for the 1962 Lotus Elan. Colin Chapman chose to use the 116E thin wall cast iron block first used by Ford in the Consul Classic, the Classic Capri and later to be used in the Cortina. While the basic engine design was relatively sound, being of 5 main bearing construction, it was by no means a performance engine. To achieve the power required, Chapman commissioned Harry Mundy, then technical editor for Autocar magazine, to design a double overhead camshaft conversion. This comprised an aluminium cylinder head and an aluminium front cover assembly containing the water pump and the chain driven camshaft drive.
In its initial evolution the engine had a cubic capacity of 1498 cc and produced approximately 100 bhp (75 kW). After approximately 50 engines had been produced (only 22 engines of this initial specification made their way into roadgoing Elans, the rest being used in the Lotus 23) the specification was changed so the engine had a 0.060" larger bore dimension as standard thereby increasing the cubic capacity to 1558 cc. This enabled an overbore of 0.040" permitted by the FIA regulations would still mean a cubic capacity below the new 1600 cc FIA class limit.
The 1558 cc twincam engine has internal dimensions as follows
3.250 inches (82.55 mm) bore
2.900 inches (72.746 mm) stroke
The 116E block was used in 5 basic versions
The cylinder head has hemispherical combustion chambers similar to that first used by Peugeot on their 1912 Grand Prix car and subsequently refined by Jaguar in their XK engine of the 1950s
Valve sizes used are 1.530" diameter inlet and 1.325" diameter exhaust on all engines except the "big valve" Elan Sprint and Lotus Europa models which have an inlet valve measuring 1.565" diameter.
The Lotus Twin Cam is an enduring engine and even to this day is still used in rallying, hillclimbing, autocross and of course, historic motorsport events. In fact, some may argue that the "twink" is more popular in motorsport now than it was during its production. This, in no small part, is due to the likes of companies such as QED Motorsport who strive to keep the engine in service with hard or impossible to find engine components. QED even bought the license to officially re-produce the Twin Cam's cylinder head.
The power output for roadgoing versions are as follows (official figures as claimed by Lotus)
100 bhp (75 kW; 101 PS) Elan 1500
105 bhp (78 kW; 106 PS) Elan 1600, S2, S3
105 bhp (78 kW; 106 PS) Elan S4
115 bhp (86 kW; 117 PS) Elan S2 S/E, S3 S/E, S4 S/E
118 bhp (88 kW; 120 PS) Late Elan S3 S/E
126 bhp (94 kW; 128 PS) Elan Sprint
Approximately 34,000