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A tuned exhaust system is an exhaust system for an internal combustion engine which improves its efficiency by using precise geometry to reflect the pressure waves from the exhaust valve or port back to the valve or port at a particular time in the cycle. Tuned exhaust systems are common on motor racing engines, light aircraft engines,〔http://www.powerflowsystems.com/ retrieved 15 May 2012〕 model engines and two-stroke motorcycle engines, and are not restricted to these applications. They are of two main types: * In a two-stroke engine, tuned expansion chambers are used to reduce loss of the new charge caused by late closing of the exhaust port by delivering a pulse of positive pressure after the exhaust gases have left the cylinder.〔http://microcarproject.tripod.com/html/tuned_exhaust_system.htm retrieved 15 may 2012〕 * In a four-stroke engine, tuned extractor manifolds are used to promote scavenging of the exhaust gases by delivering a pulse of negative pressure just before the exhaust valve closes. In either case, the efficiency of the system is greatest at a particular engine speed, which is determined by the exhaust system geometry. Tuning the system for best effect is typically done both by calculation during the design of the exhaust system, and by trial and error during engine development. An important recent development is variable geometry exhaust systems, both for two-stroke and four-stroke engines, which allow the tuning to be effective over a wider range of engine speeds. ==Two-stroke engines== (詳細はウィキペディア（Wikipedia）』 ■ウィキペディアで「tuned exhaust」の詳細全文を読む スポンサード リンク
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