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A V8 engine is an eight-cylinder V engine with the cylinders mounted on the crankcase in two sets of four cylinders, in most cases set at a right angle to each other, but sometimes at a narrower angle, with all eight pistons driving a common crankshaft. In its simplest form, it is basically two inline-four engines sharing a common crankshaft. However, this simple configuration, with a flat- or single-plane crankshaft, has the same secondary dynamic imbalance problems as two straight-4s, resulting in vibrations in large engine displacements. Since the 1920s most V8s have used the somewhat more complex crossplane crankshaft with heavy counterweights to eliminate the vibrations. This results in an engine that is smoother than a V6, while being considerably less expensive than a V12 engine. Most racing V8s continue to use the single plane crankshaft because it allows faster acceleration and more efficient exhaust system designs. ==Applications== The V8 with a crossplane crankshaft (see below) is a common configuration for large automobile engines. V8 engines are rarely less than in displacement and in automobile use have exceeded in production vehicles, such as the American Cadillac Eldorado for instance. In some applications, e.g. industrial and marine V8 engines, displacement can be even larger. In automobiles V8 engines are used in a wide variety of cars, mostly they are utilized in more powerful segments and types of vehicles, such as for example the American muscle cars, and also in sports cars, luxury cars, pickup trucks, and sport utility vehicles. Many car manufacturers offer a V8 as an option in vehicles which have a V6 or straight-6 as standard engine. Hence V8-engined cars in many countries are a symbol of exclusivity and prestige, as they are only found in upscale, high-performance premium/luxuy vehicles. In some cases, V6 engines were derived from V8 designs by removing two cylinders while maintaining the same V-angle so they can be built on the same assembly lines as the V8s and installed in the same engine compartments with few modifications. Some of these employed offset crankpins driving connecting rod pairs, enabling a regular firing sequence. The traditional 90° big-bore V8 engine, as found on many American makes, is generally too wide and too long to fit in vehicles with a transverse engine front-wheel drive layout, so its applications are limited to rear-wheel drive sports cars, muscle cars, pony cars, luxury cars and light trucks. The shorter and occasionally narrower V6 engine is easier to fit in small engine compartments, but a few compact V8 engines are used in transverse FWD and transverse AWD engine configurations in larger cars, such as Cadillacs and Volvos. These engines often have tighter cylinder bore spacings, narrower cylinder bank angles, and other modifications to reduce their space requirements. In motorsports V8s are common and have been a popular engine choice in purpose-designed engines for race-cars in many different types and classes of automotive racing, with use for example in the Formula-1 or the American NASCAR-racing league. They usually have flat-plane crankshafts, since a crossplane crankshaft results in uneven firing into the exhaust manifolds which interferes with engine tuning, and the crossplane's heavy crankshaft counterweights prevent the engine from accelerating rapidly. They are a common engine configuration in the highest echelons of motorsport, especially in the U.S. where it is required in IRL, ChampCar and NASCAR. V8 engines are also used in Australian motorsport, most notably in the V8 Supercars. Formula One began the 2006 season using naturally aspirated V8 engines, which replaced the V10 in a move to reduce costs and power. Medium-weight trucks tend to use the straight-6 configuration since it is simpler and easier to maintain, and because the straight-6 is an inherently balanced layout which can be scaled up to any size necessary. Large V8s are found in the larger truck and industrial equipment lines. Although it was the early choice for aircraft engines, the V8 engine is seldom used in modern aircraft engine as the typically heavy crankshaft counterweights are a liability. Modern light planes commonly use the flat-8 configuration instead as it is lighter and easier to air cool. In addition it can be manufactured in modular designs sharing components with flat-4 and flat-6 engines. One of the few V8 engines used for aircraft propulsion in the World War II years was the German inverted V8 configuration, air-cooled Argus As 10 powerplant. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「V8 engine」の詳細全文を読む スポンサード リンク
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