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All about variable valve timing

Question : I WILL be in the market for a new car soon. I have been told that the latest engines come with Variable Valve Timing technology that makes the vehicle more powerful and saves on fuel. Please elaborate on what variable valve timing is and how it works.

Answer : VARIABLE Valve Timing (VVT), as the name suggests, varies the valve timing of the engine.

There are varying flavours of WT depending on the vehicle manufacturer, and they are known as VTEC, VVTi, VVTi-L, DVVT, etc, but they all function to vary the valve timing or valve lift, or both.

For smooth engine operation at low speeds, valve overlap must be kept small and lift low. The opposite is true for high engine speed operation. The result of using a large valve overlap and high valve lift at low speeds is rough running, and in extreme cases, backfire through the exhaust.

VVT can be applied to the inlet valves, exhaust valves or both. The variation in timing can be either on-off or progressive, and can either be mechanical, hydraulic or electronically controlled.

WT does increase engine output, reduce exhaust emissions and increase fuel economy.

 
   
 

All about variable valve timing

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