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because all of those things (minus compression) add flow through the motor. Adding more air will give you the ability to make more power. The 3 stage manifold adds more flow. you can get more power out of many cars by adding an intake and exhaust, without touching compression or valve lift. Everyone knows this. Adding the manifold is another way to increase flow.
Valvetronic adds both lift AND duration (though not separately). When valvetronic increases lift at the valve, it also increases duration at the same time. You are basically taking the base cam profile and applying a modifier to it, like base lift and duration X 1.5 at part throttle, and X 2.0 at WOT (just an example). it's variable, not stepped like VTEC is.
The 330i runs more max lift+duration than the 325i, so changing the valvetronic program is like changing the camshaft on a regular car.
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