Geezer, if your bike is an 03' TBA it is a 790cc (NOT 865cc) so you have the good cams and will notice a big difference with mods etc. The 865cc came to the speedmaster in 05' and the TBA in 07'.

It's best to start with all the add ons as greybeard mentioned (pod filters exhaust needles jets etc.) and then if you still need more power like I did, get a wiesco 904cc BB kit and port the cylinder head to get somewhere like a 40-50% increase on stock!

TBA, Stainless extractors / drag pipes, 65mm over forward controls, Thruxton needles, 904cc, head ported, lowered 1-inch, Console removed, relocated battery box, Australia.