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The straight-4 is by far the most common 4 cylinder configuration, whereas the straight-6 has largely given way to the V6, which although not as naturally smooth-running is smaller in both length and height and easier to fit into the engine bay of smaller modern cars. Some manufacturers, notably Audi, VW and Volvo, have also used straight-5 configurations.
Many manufacturers mount straight engines at an angle from the vertical, referring to them as slant engines. Chrysler's famous Slant 6 was used in many models in the 1960s and 1970s. Honda also often mounts their straight-4 engines at a slant, as on the Honda S2000. SAAB first used an inline-4 tilted at 45 degrees for the Saab 99, but later versions of the engine was less tilted.
A straight engine is considerably easier to build than an otherwise equivalent horizontally opposedA flat engine or boxer engine or horizontally opposed engine is a type of engine where the pistons lie horizontally opposed, with pairs of cylinders on the left and the right, as opposed to most modern engines where the alternating pistons are positioned or V engineA V engine is a common configuration for an internal combustion engine in which the pistons are aligned so that, if viewed along the line of the crankshaft, they appear to be in a V. The V configuration reduces the overall engine length and weight compare because the cylinder bankPiston engines are typically arranged with their pistons in rows, moving inside individual cylinders. This allows the engine block to be built from a single piece of metal, which is machined. Engines often have more than one row of pistons, each with thei can be milled from a single metal casting and it requires fewer cylinder headsBMW In an internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the combustion chamber and the location of the valves and spark plugs. The top half of the cylinder head contains the camshaft in and camshaftsThe camshaft is an apparatus used in piston engines to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves. Inline engines are also much smaller in volume than designs like the radialbiplane The radial engine is a configuration of internal combustion engine, commonly used in aircraft, in which the cylinders are arranged pointing out from a central crankshaft like the spokes on a wheel. The cylinders are connected to the crankshaft wit, and can be mounted in any direction. Straight configurations are simpler than their V-shaped counterparts and usually provide smoother running, but at the cost of greater engine length.
Two main factors have led to the recent decline of the straight-6 in automotive applications. Lanchester balance shafts, an old idea reintroduced by Mitsubishi in the 1980s to overcome the natural harshness of the straight-4 engine and rapidly adopted by many other manufacturers, have made both straight-4 and V-6 engines much more refined than used to be the case. The inherent smoothness of the straight-6 is no longer as great an advantage as it used to be. Secondly, at around the same time, fuel consumption became a much more important factor. Cars became smaller and much more space-efficient. The engine bay of a modern small or medium car, typically designed for a straight-4, often does not have room for a straight-6, but can fit a V-6 with only minor modifications. Conversely, if the car is designed to have enough room for a straight-6, the 4-cylinder version of the same car will have wasted space and, all else being equal, cost a little more to manufacture and use more fuel.
Some manufacturers (originally LanciaLancia is an Italian automobile manufacturer founded in 1906, part of the Fiat group since 1969. During the 1980s the company cooperated with Saab Automobile, with the Lancia Delta being marketed as Saab 600 in Sweden. Saab also helped with the logistics, and more recently VolkswagenVolkswagen VW is an automobile manufacturer based in Wolfsburg, Germany. It forms the core of VAG, one of the world's four biggest car producers. Origins in 1930s Germany The origins of the company date back to 1930s Nazi Germany, and the project to build with the VR6) have attempted to combine advantages of the straight and V configurations by producing a narrow-angle V; this is more compact than either configuration, but is less smooth (without balancing) than either.
Straight-6 engines can still be found in cars like the Australian Ford Falcon and the BMW 6-cylinder models.