C36 engine swap is the typical choice to go with, IF you have a complete donor car and a 1995 model one at that too. Apart from the engine from that donor, you will need the ECU, wiring loom and the 2.87 rear diff as majority of them had ASD too. I don't know what engine you have at the moment, but if its a 320 then you could build your own twin turbo setup on that. Aim for 350bhp via a piggy back ECU or even a complete standalone system, and it'd pretty much p*ss all over a C36. You'll be into V8 territory.