The Lotus-Ford Twin Cam is an inline-four petrol engine developed by Lotus for the 1962 Lotus Elan. A few early examples displaced 1.5 litres, but the majority were 1.55-litre (1557cc) engines. It used a Ford "Kent" iron cylinder block and a new aluminium cylinder head with dual overhead camshafts. The Twin Cam was used in a variety of vehicles until Lotus stopped production in 1973. It was succeeded by the Lotus 907 engine.
History For the Lotus Elan, Lotus founder Colin Chapman wanted to find a less expensive engine than the costly all-alloy Coventry Climax FWE used in the original Lotus Elite. He felt that basing his new power-plant on an engine built in large volumes would keep costs down.
Chapman initially chose the Ford Kent inline-four used in the Ford Anglia as the basis of this new engine. The original Kent displaced and had a cast iron block produced with Ford's thin-wall casting process, resulting in a relatively light part. While the original block only provided three main bearings for the crankshaft, the oversquare design kept piston speeds down and gave room for larger valves in the new cylinder head. When the larger Kent engine for the Ford Consul Classic 109E was released, it became the platform for most of the development of the new Lotus engine.
Engine designer Harry Mundy had been working on two projects for Jean Daninos' Facel S.A. One design was an all-new quad-cam V6 displacing under 3.0 litres. The other was a new DOHC cylinder head to replace the failure-prone original on the 1.6-litre inline four Pont-à-Mousson engine used in the Facellia. Financial problems at Facel kept either engine from reaching production, but when Chapman found out about the smaller engine he commissioned Mundy to adapt the Facellia design to the Ford engine block. Mundy's design for Lotus comprised an aluminium cylinder head and an aluminium front cover and its back plate assembly containing the water pump and the camshaft drive chain.
After the initial design was finished, outside consultant Richard Ansdale produced detailed drawings of the new cylinder head. Lotus employee Steve Sanville headed the production engineering team that included Mike Costin, Neil Francis and Bob Dance. Harry Weslake conducted a flow bench analysis on the early head. Early Twin Cam prototypes had problems at the head joint. Keith Duckworth, who had already left Lotus for Cosworth Engineering, was brought back to look at the new cylinder head. Duckworth made several design changes, reshaping the ports and adding structure to the head.
The first Lotus Twin Cam engine was fired up on a test bench on October 10, 1961. This engine broke a crankshaft during testing; a failure blamed on the three main-bearing block. The first test vehicle to receive a Twin Cam was a left hand drive Ford Anglia, and the engine was installed on 18 January 1962. This Anglia is reported to have overtaken a Jaguar at well over in the hands of Jim Clark on his way home to Scotland from Goodwood.
In May 1962 Ford announced the 1498cc Kent engine. This engine first appeared in the Consul Classic/Capri 116E in August 1962, and then in the Cortina 1500 Super in January 1963. The engine had a taller deck height than the earlier Kent engines, and with a bore and stroke of , capacity was . Its crankshaft was carried in five main bearings. Power output was about at 4600 rpm. As soon as a block could be obtained work began to convert the Lotus cylinder head to the five-bearing, 1498 cc block. Duckworth assembled the first two production-specification engines, one of which powered a Lotus 23 on its racing debut at the Nürburgring. After building a limited number of 1.5 L Twin Cams, the bore was increased to , raising the capacity to 1.56 L.
Assembly of the first 50 engines was contracted out to J.A.Prestwich. Prestwich also machined the raw cylinder head castings (cast by William Mills) on these early twin cam engines.
The Twin Cam had its official debut at the Earls Court Motor Show in October 1962. Total production of the engine was approximately 34,000 units, in 24 different varieties.
Engine name Chapman named the engine the "Lotus Twin-Cam" at its introduction in 1962 and Lotus continued to use that name. When production switched from the Cortina-Lotus to the Ford Cortina Mark II-based Cortina Twin Cam in 1967, Ford began to call the engine the "Lotus-Ford Twin Cam". The engine is also known informally as the "Lotus TC" or the "Twink".
Successors The Lotus 900 series of engines replaced the Twin Cam in Lotus' cars after 1973; Lotus ended production of the Twin Cam in 1975.
In 1977 it was announced that Caterham Cars had taken over the rights to build and develop the Twin Cam engine, using Ford blocks. Caterham also had the big-valve version (with twin Dell'Orto carburettors) emissions tested and obtained a certificate of compliance. Caterham had engine tuners Vegantune build them engines using reconditioned twin cam heads to supply the very important Japanese market. Caterham also had Vegantune develop a version of the Twin Cam using Ford's 1598-cc block (rather than basing it on the earlier 1498 cc unit) with their own, improved DOHC cylinder head. Called the VTA, this variant launched in 1983. Supplied to Caterham Cars as a replacement for the Twin Cam in the Caterham Seven, the VTA featured belt-driven cams. The engine used the later Crossflow block and displaced 1.6 or 1.7 litres. Power was . Around 40 units were supplied to Caterham but quality control was very uneven and Caterham eventually switched over to the Cosworth BDR or the single-cam 1700 Supersprint.
Technical The Twin Cam's displacement is usually rounded up to . Its bore and stroke are respectively, for an actual displacement of . This allowed the Twin Cam to be over-bored by up to and still remain below the 1600 cc class limit permitted by FIA regulations. The over-bore limit of 1 mm is also stated in the FIA Homologation papers with the resultant displacement of 1,595 cc (83.55 mm x 72.75 mm, 1,595.42 cc).
The cylinder head has hemispherical combustion chambers (correct statement would have been "pear shaped chambers" since this has implications on the angle of the valves). Valve sizes are diameter inlet and diameter exhaust on all engines except the later "Big Valve" engines. The valve stem axis is inclined 27° from vertical on both intake and exhaust. Initial cam timing was 15/53/53/15 with the same cam profile as the ET418 Coventry Climax FWE cam, which resulted in at 5700 rpm for the 1,498cc engine with a 9.5:1 compression ratio. 1,557cc production engines had 22/62/62/22 cam timing with lift (developed by Cosworth as 'CPL1' -Cosworth Production Lotus) with 9.8:1 compression ratio.
The water pump used the engine front cover as its housing, making water pump replacement difficult. The intake manifold was a series of short tubular stubs cast as an integral part of the cylinder head. The heads for 175CD Zenith-Stromberg carburettor had two siamesed stubs (part of the head casting), making them not interchangeable with earlier heads using Dell'Orto DHLA40 or 40DCOE Weber carburetors, whose intake was four individual tubes (also part of the head casting). Exhaust gases were handled either by a cast-iron manifold or a fabricated tubular header, depending on application.
The original in-block camshaft was retained and, as in the original 116E, drove the side-mounted distributor and nearby external oil pump/filter assembly, minimizing modifications to the mass-produced iron block. The original cam along with the DOHC cam sprockets were driven by a long front-mounted, single-row Renold roller timing chain.
Early Lotus blocks were simply standard Ford production line items selected for having the thickest cylinder walls, and were identified by an "A" stamped into the timing cover mating face. Later blocks were specially cast with Twin Cam production in mind and identified by an "L" cast into the block under the engine mount. Twin Cam blocks came from 6 basic casting versions. Prior to 1968 the first 4 digits were often ground off the block and "3020" was stamped in its place.
1962 to 1967 The 116E-6015 block with round main bearing caps and 4 bolt crankshaft The 120E-6015 block with round main bearing caps and 4 bolt crankshaft 1967-1975 The 3020-6015 block with round main bearing caps and 6 bolt crankshaft The 681F-6015 block with round main bearing caps and 6 bolt crankshaft The 681F-6015 block with square main bearing caps and 6 bolt crankshaft The 701M-6015 block with square main bearing caps and 6 bolt crankshaft
Early engines used a crankshaft, connecting rods and pistons from Lotus. The crank was cast iron, and the pistons had a slight crown and were fly-cut to clear the valves. A revised Twin Cam was released in 1966. In this version the fly-cuts were smaller, and the con-rods were Ford 125E parts. The flywheel was also attached to the crankshaft by six bolts, an increase of two over the previous model. The Twin Cam had a problem with oil surge, and the attachment of the starter motor was subject to flexing when trying to spin the high-compression engine.
Early engines had the word "Lotus" in script cast in raised letters on the cam cover above each camshaft. Later engines had a raised border across the front of the cam cover with the word "Lotus" cast in raised text set within it. The portion of the cover over the cams was smooth.
Special Equipment tune
Lotus began to offer more highly tuned Special Equipment engines as options in their cars. The parts for these engines could also be bought from Lotus Components Ltd. At first, these were Cosworth developed and assembled engines with cast cranks and Cosworth name plates on the cam cover. Duckworth was responsible for the design of the Special Equipment cams. Cosworth later distanced themselves from this business, and Lotus started selling equivalents. BRM Phase I received BRM camshafts and high compression cast pistons, and BRM Phase II added Mahle forged pistons, BRM forged conrods, small-end bushes and big-end bolts to the Phase I. When offered in assembled form, these engines carried a BRM name plate on a specially cast 'BRM' cam cover, but the actual assembly of these high performance 'BRM' road engines was carried out by the BRM Engine Development Division of Rubery Owen & Co. Ltd., an affiliated company of BRM through its ownership, not by BRM itself. The Special Equipment ('S/E') engines had 26/66/66/26 cam timing.
Originally applied to tuned Elans and Lotus Cortinas, the term "Special Equipment" was later used by Lotus to designate those Series 2 and later Elans with higher output motors, and are referred to as Elan S/Es.
SSE In 1968 Sanville began building a series of Twin Cams using a new camshaft called the Super Special Equipment cam, or D-Type, that was based on the Coventry Climax FWA 3060 cam. Heads used in SSE engines were shaved by , boosting the compression ratio to 10.3:1. The ignition was advanced slightly, and larger chokes and different jets were fitted to the Weber carburettors. Power was estimated to be , fully three years prior to the release of the Big Valve engine. Some SSE engines are said to have left the factory in Super Weber S/E Elans.
Big Valve engine
The Big Valve Twin Cam was a project of Lotus' Engineering Director Tony Rudd. Rudd reduced the deck height by to raise the compression ratio to 10.5:1, increased the diameter of the inlet valves to , modified the inlet runners' shape for the larger valves and installed Super Special Equipment D-type camshafts. Power was increased 20% over the regular engine's . Big Valve engines were offered in the Elan Sprint, Elan +2 130, and Lotus Europa Twin Cam Special models. Cam covers for Big Valve engines had the words "Lotus" and "Big Valve" cast in raised letters across the front of the cam cover. The portion of the cover over the camshafts had raised ribs cast in.