Many fans like small steel guns - small cars to install high-power engine, with high-performance suspension adjustment and body matching, a small car inside the performance of the most outstanding category. I really like this car, the body brought a small live and free to cart can not match. And this car is not publicity, the appearance of ordinary road goods and almost the same, but if you want to break out of your passion, it can be comparable to quasi-sports car performance. I call this car as "wolf in sheep's clothing". The major companies have their own small steel guns, and the core of the competition between the focus of which is the engine. Because, in a small steel gun, the power is not by the displacement of the engine can be resolved.
    Ordinary mass production of small cars (referring to A or A level of the following models) of the engine generally inline four-cylinder arrangement, but the inline four-cylinder engine power is often limited, can not meet the performance requirements of small steel gun.
    Does that consider choosing to install a 6-cylinder engine? This will also encounter problems.
    Most small cars do not have enough space to install a 6-cylinder engine. At present, the mainstream 6-cylinder engine has V-and inline two kinds of arrangement, their size is very large, only suitable for installation in large and medium-sized car. The vast majority of small cars due to the use of front engine and front wheel drive in the form of the engine, gearbox, differential assembly installed in the front axle before. At the same time, in the former engine compartment is also equipped with abs pump, server, battery, steering mechanism and so on, will take up the small car engine compartment this poor space. So it is difficult for the designer to install a 6-cylinder engine (especially the in-line 6-cylinder engine, because it is larger) installed on a small car.
    From the vehicle characteristics, small cars are more suitable for the use of transverse engine design. Of course, there are special cases, such as the BMW 3 such a long nose compact car on the use of the longitudinal engine, but the drawback is that the vehicle space utilization is very low, not suitable for mainstream civilian small car design trend. Inline 6-cylinder engine length is very large, if the tap design, the engine compartment simply can not accommodate. The width of the V6 engine is equivalent to the width of the two inline engines, depending on its exact angle design (usually 60 degrees or 90 degrees), so it is smaller than the space occupied by the inline 6-cylinder engine. And V6 engine exhaust pipe from both sides of the engine discharge, exhaust efficiency is high. Even so, as mentioned above, the width of the V6 engine is equivalent to the width of two inline engines, which also exceeds the width that the small car's engine compartment can accommodate, so the V6 engine can not be accommodated on most small cars.
    In order to solve this contradiction, the German Volkswagen in 1991 developed a small angle (15 degrees) V6 engine, and it assembled in the third generation of golf, to replace the previous 2.8-liter V6 engine, which is often heard Said "VR6". VR6 engine is a true compact design, the angle is almost close to the inline engine, but only slightly longer than the inline four-cylinder engine, so it can match the vast majority of small cars, even including the A0 level POLO (POLO did not install this The engine is because the cost is too high). Mercedes-Benz V series, due to its short design, can not install Mercedes-Benz V6 engine, also used the VR6 engine to match. VR6 although only the use of the angle of 15 degrees, but because the cylinder and the cylinder is staggered, so there is a very wide gap between the cylinder (as shown below), although its length has increased, but its width is only equivalent to V6 Half of the engine.
    VR engine asymmetric structure (from left to right followed by L4, V6, VR6)
    VR6 engine is another important feature of its 24-valve design and W-type structure. With the ordinary V-type engine, VR6 is used in asymmetric design. The cylinder and the cylinder are intertwined, which means that the fresh air introduced from the intake manifold is difficult to enter the outside intake manifold (otherwise it is difficult for the exhaust gas to be collected from the inside intake manifold to the exhaust manifold). As shown below:
    VR6 engine side for intake, one side for exhaust. Because of its asymmetry, the intake and exhaust system is unusually complicated to occupy a large amount of space in the cylinder head, making the cylinder head around the high temperature, but this design saves a lot of space.