I think to build a 650hp engine and have it reliable you will need nikasel liners aswell £1600+

head and cams that is ready to go for 650hp £2000

Inlet manifold and Injectors Sweedish style £1000

Turbo, wastegate, exhaust manifold £2500

Custom made Exhaust System to flow 650hp £1100

where do you stop

to be honest if you was to use your current engine with a bigger ported head and just strap a GT35 on it and have it mapped on L8 i dont think you will see 650HP and it will probebly Surge its tits off ohh and push a rod through the side of the block if you want a 650hp engine you have to have a 650hp engine built in the first place look at some of the most powerfull engines about! Yum, Ade, Martin reyland, AndrewG Focus, All hand built for the job not just boltd together

tell you somthing if you can do it i will be right behind you