Vauxhall Slant-4 engine

The Slant Four is a type of car engine manufactured by Vauxhall Motors and, in modified form, by Lotus Cars. Unveiled in 1966, it was one of the first production overhead camshaft designs to use a rubber toothed belt to drive the camshaft from the crankshaft^[1] a method developed in 1956 by Bill Devin.

Vauxhall

The engine features four inline cylinders inclined at an angle of approximately 45 degrees (hence the name), and this is because Vauxhall had originally planned to develop a whole family of engines all built on the same production line. There was to be slant four and V8 versions in both petrol and diesel versions, designed under the guidance of Vauxhall's then chief engineer, John Alden. Although several diesel 4-cylinder and a V8 petrol engine prototypes were built only the 4-cylinder petrol made it to series production. There is a single overhead camshaft operating two valves per cylinder. An ingenious valve train design incorporating an inclined socket head cap screw, allowed valve clearances to be adjusted with a feeler gauge and an Allen key. The block and crossflow head are both of cast iron. The layout makes good use of the cylinder inclination to lower the overall height of the engine, which allowed for more aerodynamic designs of cars to be achieved by lowering the bonnet line. It also means most of the engine is very easy to access for maintenance, with the exception of the exhaust manifold and spark plugs, which are "underneath" the slanted cylinders.

Although prototype engines were fitted to the FC 101 Victor the first production car to use the engine was the 1967 Victor, at capacities of 1599 cc and 1975 cc. Later, for launch of the FE Victor in 1972, the smaller engine was increased to 1759 cc, and the larger, to 2279 cc. Bill Blydenstein Racing developed a long stroke version with a capacity of 2600 cc, in which form it could produce almost 250 hp (190 kW). Having originally been designed as the basis of a future V8, the block is immensely strong and can handle huge increases in power without modification, also the crank was designed to be shared with the diesel version which meant in built strength was assured for the petrol versions. The larger capacities are renowned for their immense torque (having such large pistons), but a downside of this is that they are not very smooth running or high-revving, and lack balance shafts. A fuel injection version of the 2.3-litre engine was planned for both the HP Firenza and VX4/90 and running prototypes were tested the project was abandoned due to cost and the impending merger of Vauxhall's design and engineering with that of Opel in Germany.

The engine was widely used in many models of car, and was also developed into a marine engine for boats and was popular with amateurs due to its great strength, tunability and simplicity. The engine was still being manufactured well into the 1980s for the Bedford CF van, and many of them are still in daily use.

Ultimately however, the Slant-4 gained a less favourable reliability record than its in-house contemporary in the GM Europe stable - the Opel CIH (Cam In Head) unit - although it was arguably more technically advanced. The Slant-4 was abandoned for the newer generation of badge engineered Vauxhalls from the mid 1970s onward; the Cavalier Mk.1 used the CIH units, whilst the Bedford CF van also lost the Slant-4 in favour of the CIH in its facelifted form in 1983.

Lotus 900 series engines

It is said that when Vauxhall unveiled its new slant-four engine at the 1966 Earls Court Motor Show its bore centers were exactly the same as those proposed by Lotus for their new all-alloy engine. Lotus boss Colin Chapman immediately negotiated a deal with Vauxhall to buy some of their cast-iron blocks so that development of Lotus’ own aluminum 907 engine could be sped up.

The design became the basis for the Lotus 2.0 and 2.2 engines used in a wide variety of sports cars, but the basic block was cast in aluminium alloy instead of iron, which made it considerably lighter. The Lotus engine also used a different cylinder head of light alloy, featuring double overhead camshafts and four valves per cylinder. The engines were so close in design that, with a few modifications, the Lotus head can be fitted to the Vauxhall block; engines with Lotus heads were used in Vauxhall's dealer team race and rally programmes until the late 1970s.

Vauxhall 16-valve engines

Following experiments with an eight valve twin cam cylinder head for the Vauxhall Slant Four, the company developed a 16-valve, twin cam engine in the early 1970s; the first test engine, 'Old Number 1', was running by 1973. The cylinder head was similar in design but different in appearance to the Lotus one; in particular the cam carriers on the Vauxhall engine were angled upwards so that the covers were both horizontal (those on the Lotus engine were equal about the cylinder centreline).

The 16-valve engine was first used in the Chevette 2300 HS, but initially heads were in such short supply that road car production was delayed and the rally team continued to use the Lotus heads they were familiar with. This led to the cars being prevented from starting the 1978 Rally of Portugal after protests from other teams. As a result, all cars competing in international rallies were forced to use the Vauxhall head, and Blydenstein Racing, the company running the rally team, improved it to a point where it performed better than the Lotus head.

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