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The five-cylinder engine's advantage over a comparable four-cylinder engine is best understood by considering power strokes and their frequency. A four-stroke cycle engine fires each cylinder once every 720 degrees — the crankshaft makes two complete rotations. If we assume an even firing engine, we can divide 720 degrees by the number of cylinders to determine how often a power stroke occurs. For a four-cylinder engine, 720° ÷ 4 = 180° so there is a power stroke every 180 degrees, which is two power strokes per revolution of the crankshaft. A V8 engine gets a power stroke every 90 degrees: 720° ÷ 8 = 90°, which is four power stokes for each revolution of the crankshaft.
A given power stroke can last no more than 180 degrees of crankshaft rotation, so the power strokes of a four-cylinder engine are sequential, with no overlap. At the end of one cylinders power stroke another cylinder fires.
In a one, two, or three cylinder engine there are times when no power stroke is occurring. In a three-cylinder engine a power stroke occurs every 240 degrees (720° ÷ 3 = 240°). Since a power stroke cannot last longer than 180 degrees, this means that a three-cylinder engine has 60 degrees of "silence" when no power stroke takes place.
Five-cylinder engines have a crank with 72 degree angles (except for the VW V5, that has an offset in the crank that corresponds to the angle between the cylinders. Despite the V configuration the engine has even firing intervals.). Most five cylinder engines have the firing order 1-2-4-5-3. Firing of one cylinder after another (e.g. 1-2-3-4-5 in case of a five cylinder engine) is never used except in 3 cylinder engines where there is no alternative. The reason for this is that the resulting engine will have a strong tendency of rocking from end to end, as well as having generally poor balance.
A five-cylinder engine gets a power stroke every 144 degrees (720° ÷ 5 = 144°). Since each power stroke lasts 180 degrees, this means that a power stroke is always in effect. Because of uneven levels of torque during the expansion strokes divided among the five cylinders, there are increased secondary-order vibrations. At higher engine speeds, there is an uneven third-order vibration from the crankshaft which occurs every 144 degrees. Because the power strokes have some overlap, a five-cylinder engine may run more smoothly than a non-overlapping four-cylinder engine, but only at limited mid-range speeds where second and third-order vibrations are lower.
Every cylinder added beyond five increases the overlap of firing strokes and makes for less primary order vibration. An inline-six gets a power stroke every 120 degrees. So there is more overlap (180° - 120° = 60°) than in a five-cylinder engine (180° - 144° = 36°). However, this increase in smoothness of a six-cylinder engine over a five-cylinder engine is not as pronounced as that of a five-cylinder engine over a four-cylinder engine. The inline-five loses less power to friction as compared to an inline-six. It also uses fewer parts, and it is physically shorter, so it requires less room in the engine bay, allowing for transverse mounting.
A five-cylinder engine is longer and more expensive to manufacture than a comparable four-cylinder engine, but some manufacturers feel these costs are outweighed by its greater capacity in a smaller space than a six-cylinder.
From the standpoint of driving experience, five-cylinder engines are noted for combining the best aspects of four- and six-cylinder engines. They generate more power and torque than four-cylinder engines, while maintaining better fuel economy and "pep" than six-cylinder engines. Five-cylinder turbos have been used on more than one occasion in sport and racing applications for their balance of performance qualities. The Volvo S60 R has a 2.5 litre turbocharged inline-five–cylinder engine which is capable of generating 300 brake horsepower (224 kW) and 295 lbf·ft (400 N·m) of torque across a large amount of its rpm ranges. The new Ford Focus RS performance car uses the same Volvo 5-cylinder engine, developed (by Ford) to very similar power levels, and is one of the most powerful FWD production cars ever created. Another example of a high power 5 cylinder car is the Audi RS2, with its 2.2 turbocharged engine making 311 hp.
A disadvantage of a straight-five over a straight-six engine is that a straight-five engine is not inherently balanced. A straight-five design has free moments (vibrations) of the first and second order, while a straight-six has zero free moments. This means that no additional balance shafts are needed in a straight-six. By comparison an inline-four engine has no free moments of the first or second order, but it does have a large free force of the second order which contributes to the vibration found in unbalanced straight-four designs.[3]
The use of straight-five petrol engines in mass production cars only became truly viable with the advent of reliable fuel injection. A five-cylinder engine using a carburetor fuel system has an unavoidable problem in that the length of the inlet manifold between the carburetor varies too greatly between cylinders at the ends of the engine and those nearer the carburetor for reliable and consistent fuel delivery. Using multiple carburetors (two or three) always results in one carburetor feeding more cylinders than the other, which also produces running and tuning problems. In theory individual carburetors could be used for each cylinder, but this approach is expensive and still brings with it the attendant difficulties in balancing the multiple carbs. Multi-point fuel injection circumvents all the above problems by feeding each cylinder individually from a central, single pump. This fuelling issue was never present in diesel engines (except the Volvo D5) which used direct injection from the very start, which is why large five-cylinder diesels were commonly seen decades before the type's adoption for automotive use.
The inline-five is known for its characteristic sound. Unlike other engine configurations, the inline-five's sound can be approximated by doubling the cylinders.
