VANOS and double VANOS are basically the same thing only applied to one or two camshafts.
In vanos engines the intake camshaft is twistable to provide variavle valvetiming.
In double vanos engines both intake and exhaust camshafts are twistable.
vtec is different, the cams in vtec engines have double sets of camlobes. At a certain rpm and when certain criterias are met it switches over.
This means the that both valvetiming and valve lift is variable (between two fixed values). In reality it is like haveing an econo cam when you are not going flat out, and when you open up you have a hotter cam.
BMW's valvetronic engines have variable valve lift.
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1994 Arcticsilber M3, 286hp, 18" AC Schnitzer wheels.