Searching for more engine power some mechanics overlook one of the easiest steps to get more power. Even if you're keeping the engine at the stock displacement, selecting a thinner 'race' cylinder-head gasket will add compression. Most modern motorcycles can easily accommodate a compression increase. This upgrade is very reliable and overall riding comfort is not affected. Higher compression ratios will dramatically increase power, but sophisticated ignition timing is required to reduce or eliminate pinging (detonation), the great engine destroyer.
Depending on the compression ratio you start from, ratios above 10.5:1, with some going as high as 12:1, will reduce engine part longevity, but is the way to go if you're looking for a blaster as opposed to high-kilometer riding.
Machining the head gasket surfaces reduces the volume of the combustion chamber, thereby increasing the engine's compression because the same volume of fuel and air must be compacted into a smaller chamber. Milling around 1mm from a 9:1 compression ratio cylinder-head will result in a 10:1 compression ratio. If you're replacing the pistons or increasing the displacement of your engine, then milling of the cylinder-head may not be necessary since higher compression pistons are often available, as well as some other sizes. High compression pistons have a higher piston dome incorporated into their design. Some have innovative dome designs that promote superior flame travel and a higher percentage of burn, therefore increasing horsepower using the fuel/air mixture already there.
If one of these sizes is what you're after, this is the way to go since forged high-compression piston cost is usually the same as the stock compression piston. Milling is still an option when looking for a ratio that is not provided for with existing manufactured pistons.