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A Honda K24A Engine with i-VTEC. VTEC (described as Variable Valve Timing & Lift Electronic Control, but stands for Valve Timing Electronically Controlled) is a system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low RPM.
For twin-cam or DOHC engines, VCT was used on either the intake or exhaust camshaft. (Engines that have VCT on both camshafts are now designated as Ti-VCT.↓) The use of variable camshaft timing on the exhaust camshaft is for improved emissions, and vehicles with VCT on the exhaust camshaft do not require exhaust gas recirculation (EGR) as retarding the exhaust cam timing achieves the same ...
MultiAir technology can increase power (up to 10%) and torque (up to 15%), as well as reduce consumption levels (up to 10%) and emissions of CO 2 (up to 10%), particulates (up to 40%) and NOx (up to 60%) [3] [7] when compared to a traditional petrol engine. The system also provides smoother cold weather operation, greater torque delivery, and ...
The Alfa Romeo Twin Spark engine, introduced in the 1987 Alfa Romeo 75, also uses variable valve timing. [3] [4] The Alfa system varies the phase (not the duration) of the cam timing and operates on the inlet camshaft. [5] Alfa Romeo's variator is a cylindrical chamber that contains a pressure chamber and piston along with helical splines.
The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary to achieve the desired result in intake and exhaust efficiency . This has been described ...
When brakes are applied, the IMA system shuts off the engine and conserved power from the electric motor is utilized. This minimizes vibration of the car body and saves fuel when the engine is idling. When the brakes are released, the electric motor will restart the engine. [10] Among the Honda car models that are using IMA: [13] [14]
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In an external combustion engine, such as a steam engine, the control of the valve timing is by the valve gear. In a typical piston valve arrangement, the timing of the intake and exhaust events for each cylinder are inextricably related as they are governed by the movement of a single piston uncovering two ports. However, the duration of the ...