A fitting guide can be found in the tech section
Once the building blocks of the breathing are complete more power can be gained without taking the engine apart by simply dropping in a new camshaft.
Camshafts get more power by having a different profile to the standard one which changes valve opening times and distance (duration and lift). I won`t go into the details of cam timing here, I`ll just say believe the manufacturers in that they get more power.
My personal preference is Piper, but there is also Kent and others from Germany and America (Techtonics etc.). The only hint I can give is if you want power go for a wilder cam than you think you should. The mild road cams for instance really will be just that – mild. I have a fast road/rally cam and once the engine is warm will idle fine at just below 1000rpm. The only thing to watch out for is with a wild cam hp is increased at a high point in the rev range whereas the power is usually lost in the lower band. This can be helped with a vernier pulley and a proper rolling road setup however.
If you do decide to fit a cam then it is pointless to do it without fitting a vernier pulley at the same time, they are expensive for what they are but as far as cost per hp they are actually quite cheap. Gains like 7 bhp @wheels are easily achievable with a good rolling road setup.