This is a very extensive procedure, on the front wheel drive versions of the 60 degree block, it is required to remove the engine from the car. A cam upgrade is one of the best choices for overall power. It can change the characteristics of the motor, by changing the power band. If you have the time and money, this is hard to beat. Make sure you choose the cam that is right for your application though, since a boosted car will want different cam specs than an NA setup. It is recommended to talk to a machine shop (if they are doing the work), or to the cam manufacturer before choosing a cam.
For those of you who are wondering exaclty what a camshaft does for extra horse power, ill try to explain it. The purpose of a camshaft in any car, is to determine when the intake and exhaust valves should be open, how much they should be opened, and for how long. Aftermarket camshafts usually open the valves more and for a longer period of time. For a good explanation, go here .
Computer controlled vehicles require a special kind of camshaft designed to produce more power, and still pass emissions. Keep this in mind when purchasing any Camshaft from any manufacturer.
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S-Series.org has a page up for different cam grinds to be used with desktop dyno. You can check those out here