Straight-4 Guide, Meaning , Facts, Information and Description
The straight-4 or inline-4 is an internal combustion engine with four cylinders aligned in one row. This is the most common configuration used in carss with an engine size up to 2.0, in some cases up to 3 litres displacement.The straight-4 engine is not a balanced configuration and while this is tolerable in a small, low-displacement, low-power configuration the vibrations get worse with increasing size and power. Most straight-4 engines below 2 litres in displacement rely on the damping effect of their engine mountings. Today most engineers will use of balancing shafts above that limit. A 4-cylinder engine needs twin balance shafts, rotating at twice the crankshaft frequency, to be smooth. Nonetheless, they were several samples of larger Straight-4s in production using no balance shafts like the 2 347cc engine that was last evolution of the Citroën DS engine. These engines were generally the result of a long incremental evolution process and they power was kept relatively low reguarding their capacity. A practical limit could be placed in the 2.4 L/2.5 L range.
Use of balance shafts allowed Porsche to use a 3 litre straight-4 engine on the Porsche 944 and other vehicles.
Racing use
1913 saw a Peugeot driven by Jules Goux winning the Indianapolis 500. This car was powered by a Straight-4 engine designed by Ernest Henry. This design was very influential for racing engines as it featured for the first time DOHC and 4 valve per cylinder.
This Peugeot was sold to the american driver "Wild Bob" Burman who broke the engine in 1915. As Peugeot couldn't deliver a new engine during World War 1 Burman asked Harry Miller to build a new engine. With John Edward and Fred Offenhauser, Harry Miller created a Peugeot-inspired Straight-4 engine. This was the first version of the engine that would dominate the 500 miles until 1976 under the brand Miller and later Offenhauser.
Another engine that played an important role in Racing history is the Straight-4 Ferrari engine designed by Aurelio Lampredi. This engine was originaly designed as a 2 litres Formula 2 engine for the Ferrari 500 but evolved to 2,5 litres to compete in Formula 1 in the Ferrari 625. For sports car racing capacity was incresed up to 3,4 L for the Ferrari 860 Monza.
Its main competitor was the Coventry Climax Straight-4 originaly designed by Walter Hassan as 1,5L Formula 2 engine it evolved the large 2495cc FPF that won the Formula One championship in Cooper's chassis.
See also: straight engine
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