How does cam timing work for a car?
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A camshaft is a spinning rod with lobes on it. Those lobes determine **when** the valves open and close. If the lobes are tall and narrow (pointy?) then they will push the valve really far open for a short period of time. If they are short and wide, the valve will only open a little bit, but for a longer period of time. Every engine is slightly different in what it needs.
The “when” is really important. Cars use a 4-stroke engine (suck, squeeze, bang, blow). You want the intake valves to be open for the first down-stroke, and closed for the other 3. You also want the exhaust valves to be open on the last up-stroke, and closed for the other 3. If any of the valves are open when the piston is near the top, they might hit the piston and cause damage. While opening on the right stroke is pretty easy, the fine-tuning of how much air to let in, and how much exhaust to leave in for proper emissions/combustion-mix is much harder.
And that’s where variable valve timing comes in. Most cars sold to the public have a camshaft designed with a smooth, quiet idle and decent efficiency. But they can improve performance if they open the intake valve early to let in more air. The problem is that if they let in too much air at idle, the RPMs will increase on their own (not safe) or they have to cut ignition which makes for a loud choppy idle. If they use the “mild” cam and adjust it back and forward, they can get the best of both worlds. The VVT is a device (driven by oil pressure or an electronic motor) at the end of the camshaft that can rotate it forward or backward to make this adjustment.
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