the engine is already big enough mate,
you just need to play with the cylinder head and throttle bodies and exhaust to increase the engines CFM.
this will include opening up the ports and reshaping (please dont polish the inlet ports)
bigger valves
throttle bodies, maybe from an R1
cam regrind (nothing too serious tho!!! or you wont enjoy riding the bike)
sports exhaust system
thinner head gasket
you will be able to turn you bike into a monster with those mods, and will be cheaper than a turbo !!!
Im new on here but Iv built a few dragbikes in the past, and will be posting my current project on this forum this weekend.
yes there is no substitute for cubes but your bike already has cubes, you just need to use the cubes you have more efficiently by letting it breath better!
not only will it be the cheapest option but your bike will be a "SLEEPER"