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Recently when I visited a car showroom the salesman pitched the car by saying it has VVT technology which is superior compared to other cars.
I researched and found out that it alters the valve timings on the cylinders.
What are the advantages of VVT?
How is it done (i.e. mechanically or electronically)? A diagram would be useful!
Is it a "gimmick" or is it worth buying a car with VVT technology?
How is it different from a i-VTEC?
Variable valve timing permits an increase in the torque in the lower engine speed ranges and increased engine power in the higher engine speed range. Basically, the system alters the relative position of the inlet camshaft with respect to the exhaust camshaft corresponding to the engine operating conditions. The idea is to control how long "valve overlap" occurs.
Based on the inputs from the various sensors that are part of engine management, the engine control unit actuates a solenoid valve, which opens a hydraulic path that the engine oil flows through. The oil pressure is applied to the advance or the retard side of a camshaft actuator.
If this control happens only in intake side, it is called 'variable valve timing'. if this happens for both intake and exhaust side, then it is called 'continuous variable valve timing'.
Advantages of VVT is the possibility of having an internal EGR, better power output and fuel economy.
i-VTEC changes HOW MUCH the intake and exhaust valves can open. VVT changes WHEN the intake and exhaust ports open.
It's a lot of information to put in an answer. The short version is that by electronically changing exactly when the intake and exhaust valves open and close, you can increase the volumetric efficiency of the engine across a large RPM range. You can also do fancy things like overlapping the exhaust and intake valves so that the exhaust helps "suck" more air and fuel into the combustion chamber, thereby making more power than would normally be available.
Cars without VVT will have a much narrower power curve because they can only work optimally within a set portion of the RPM range, but VVT allows you to enlarge that range quite a bit.
As for I-VTEC, it is basically a way to modify the camshaft profile so that it lifts the valves higher than normal, allowing more air into and out of the engine per stroke. You basically have an economy-focused cam profile when driving slow, and a high-lift performance profile when going fast.
You could also call VVT "dynamic cam timing" and VTEC "dynamic cam profiling".
