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VTEC
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== History == {{Unreferenced section|date=July 2013}} VTEC, the original Honda variable valve control system, originated from REV (Revolution-Modulated Valve Control) introduced on the [[Honda CBR400|CBR400]] in 1983 known as HYPER VTEC. In the regular four-stroke automobile engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the timing, lift and duration of each valve. [[Valve timing|Timing]] refers to an angle measurement of when a valve is opened or closed with respect to the piston position (BTDC or ATDC). Lift refers to how much the valve is opened. Duration refers to how long the valve is kept open. Due to the behavior of the working fluid (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high RPM. Optimal low RPM valve timing lift and duration settings would result in insufficient filling of the cylinder with fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM valve timing lift and duration settings would result in very rough low RPM operation and difficult idling. The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough and stay open just the right amount of time for the engine speed and load in use. === DOHC VTEC === [[File:B16A 1ere génération.jpg|thumb|VTEC debuted in the B16A engine of the 1989 Honda Integra XSi.]] VTEC was introduced as a [[Overhead camshaft#Double overhead camshaft|DOHC]] (dual overhead camshaft) system in Japan in the 1989 [[Honda Integra]] XSi,<ref name="1989vtecengine"/> which used the {{convert|160|bhp|kW|abbr=on}} [[Honda B engine#B16|B16A]] engine. The same year, Europe saw the arrival of VTEC in the Honda Civic and [[Honda CRX]] 1.6i-VT, using a {{convert|150|bhp|kW|abbr=on}} B16A1 variant. The [[United States]] market saw its first VTEC system with the introduction of the 1991 [[Acura NSX]],<ref>{{cite web|url=http://www.superstreetonline.com/features/htup-0905-vtec-history-and-technology/|title=VTEC - History & Technology - Honda Tuning Magazine|date=20 May 2009|website=superstreetonline.com|access-date=27 March 2018}}</ref> which used a 3-litre DOHC [[Honda C engine#C30A|C30A]] V6 with {{convert|270|bhp|kW|abbr=on}}. DOHC VTEC engines soon appeared in other vehicles, such as the 1992 [[Acura Integra GS-R]] ({{convert|160|bhp|kW|abbr=on}}[[Honda B engine#B17|B17A1]]), and later in the 1993 [[Honda Prelude]] VTEC ({{convert|195|bhp|kW|abbr=on}} [[Honda H Engine#H22A|H22A]]) and [[Honda Del Sol]] VTEC ({{convert|160|bhp|kW|abbr=on}} [[Honda B engine#B16A3|B16A3]]). The [[Integra Type-R|Integra Type R]] (1995–2000) available in the Japanese market produces {{Convert|197|bhp|kW PS|0|abbr=on}} using a [[Honda B engine#B18C5 (Type R)|B18C]] 1.8-litre engine, producing more horsepower per litre than most super-cars at the time. Honda has also continued to develop other varieties and today offers several varieties of VTEC, such as i-VTEC and i-VTEC Hybrid. === SOHC VTEC valvetrain === {{Unreferenced section|date=July 2013}} Honda also applied the system to [[Overhead camshaft#Single overhead camshaft|SOHC]] (single overhead camshaft) engines such as the [[Honda D engine|D-Series]] and [[Honda J engine|J-Series]] Engines, which share a common camshaft for both intake and exhaust valves. The trade-off was that Honda's SOHC engines benefited from the VTEC mechanism only on the intake valves. This is because VTEC requires a third center [[rocker arm]] and [[cam lobe]] (for each intake and exhaust side), and, in the SOHC engine, the spark plugs are situated between the two exhaust rocker arms, leaving no room for the VTEC rocker arm. Additionally, the center lobe on the camshaft cannot be utilized by both the intake and the exhaust, limiting the VTEC feature to one side. However, beginning with the [[Honda J engine#J37|J37A2 3.7L SOHC V6]] engine introduced on all 2009-2012 Acura RL SH-AWD models, SOHC VTEC was incorporated for use with intake and exhaust valves, using a total of six cam lobes and six rocker arms per cylinder. The intake and exhaust rocker shafts contain primary and secondary intake and exhaust rocker arms, respectively. The primary rocker arm contains the VTEC switching piston, while the secondary rocker arm contains the return spring. The term "primary" does not refer to which rocker arm forces the valve down during low-RPM engine operation. Rather, it refers to the rocker arm which contains the VTEC switching piston and receives oil from the rocker shaft. The primary exhaust rocker arm contacts a low-profile camshaft lobe during low-RPM engine operation. Once VTEC engagement occurs, the oil pressure flowing from the exhaust rocker shaft into the primary exhaust rocker arm forces the VTEC switching piston into the secondary exhaust rocker arm, thereby locking both exhaust rocker arms together. The high-profile camshaft lobe which normally contacts the secondary exhaust rocker arm alone during low-RPM engine operation is able to move both exhaust rocker arms together which are locked as a unit. The same occurs for the intake rocker shaft, except that the high-profile camshaft lobe operates the primary rocker arm. The J37A2 is able to use both intake and exhaust VTEC by use of a novel design of the intake rocker arm. Each exhaust valve on the J37A2 corresponds to one primary and one secondary exhaust rocker arm. Therefore, there are a total of twelve primary exhaust rocker arms and twelve secondary exhaust rocker arms. However, each secondary intake rocker arm is shaped similar to a "Y" which allows it to contact two intake valves at once. One primary intake rocker arm corresponds to each secondary intake rocker arm. As a result of this design, there are only six primary intake rocker arms and six secondary intake rocker arms.
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