Slant Four

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for the similarly named (but unrelated) engine made by Triumph, see Triumph 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 1967, it was one of the first production overhead camshaft designs to use a rubber toothed belt to drive the camshaft from the crankshaft (an honor shared with the 1966 Pontiac OHC Six), a method developed in 1956 by Bill Devin and now used on almost all modern engines.

[edit] Vauxhall

The engine features four inline cylinders inclined at an angle of approximately 45 degrees (hence the name), and this is because Vauxhall developed the engine from a General Motors V8 design from the US, dropping one entire bank of cylinders. 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, which is "underneath" the slanted cylinders.

The first car to use the engine was the 1967 Victor, at capacities of 1600 cc and 2000 cc. Later, the smaller engine was increased to 1800 cc, and the larger, to 2300 cc. Bill Blydenstein racing developed a long stroke version with a capacity of 2600 cc, in which form it could produce almost 250 hp (186 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. 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. 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.

[edit] Lotus 907

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. 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 while the basic block was copied almost unchanged, it 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. Vauxhall also developed a 16-valve head for the engine in the late 1970s, which was used on the Chevette HS, but this design suffered a number of problems in use, and the Lotus head was much better - so much so that for the rally cars, Vauxhall substituted the Lotus head, breaking the rules and getting themselves disqualified for one of the rallying seasons.