What is the Difference Between a Honda IDSI & a Vtec?

Honda Motor Co. is known for its innovations in engine technology. Honda's engines are generally low-displacement while being very efficient and easy to maintain. To squeeze the most horsepower and fuel efficiency out of their engines, Honda employs a number of specialised engine setups, two which are Honda's iDSI and VTEC systems. Understanding how each system works requires knowledge of the engine's intake and ignition process.

Valve Train

An engine is composed of two primary sections: the engine block and the cylinder head. The cylinder head features a valve train composed of camshafts, springs and retainers. When the engine is in operation, the camshafts rotate. Along each camshaft are elliptical cam lobes which compress the valve springs at set intervals, allowing air and fuel to briefly enter the engine cylinder, where it can be combusted.


The air and fuel is drawn through the open valves retainer by the pistons, which are actuated up and down by the engine crank. After drawing in the air, the pistons compress it. Spark plugs are installed into the top of each cylinder. Once the piston has compressed the air and fuel mixture, the spark plug fires, igniting the mixture. This is how an engine produces horsepower.


Honda's iDSI (Intelligent-Dual Sequential Ignition) system employs two spark plugs which are diagonally opposed at the top of each cylinder. While conventional engines only feature one spark plug per cylinder which fires once for each combustion process, Honda iDSI engines fire two sparks at different points in the combustion process, allowing for a more complete air and fuel combustion. This maximises fuel efficiency, while making the iDSI a cleaner-burning engine.


Honda's VTEC (Variable Valve Timing and Lift Electronic Control) system is more performance-oriented than the iDSI. VTEC engines feature camshafts with two different sized lobes for each valve. When the engine reaches a certain RPM, the camshafts switch to the larger cam lobe, which allows more air and fuel to enter the engine cylinders, increasing maximum torque and horsepower. The dual-lobe design of VTEC cams allows the engine to attain economical efficiency and reliability at low RPMS, while providing a boost in horsepower when the engine is accelerated to redline.

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