Camshafts open and close the valves- they open the the intake valves to let air/fuel in and the exhausts to let exhaust out. To get significant gains you usually have to port the heads & intake, get a larger throttle body and upgrade the car's exhaust with headers and an aftermarket muffler system, probably larger injectors, not to mention reprogramming the ecu. It can be done, but all this isn't cheap. Swapping in new cams won't gain you much without matching them to other components- thats where the big power comes in. I'm sure that others will try to argue, but that's how it is.
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