I also think that 150BHP out of an 8v is somewhat optimistic. The level of work to squeeze that power would be immense. The head would need to be gass flowed and new, bigger valves fitted. The injection system would need to be radically modified as would the induction system to allow the required airflow. Then there is the bottom end. That would need to be made bigger and stronger with new pistons to increase the already high C\R. If you genuinly have 148BHP, then the ECU will have been modified to its limits anyway.
To convert to turbo, or supercharger, you would need to lower the C\R and replace the pistons with items that can take the extra heat of combustion. New pistons are not cheap, and neither is the kit for turbo or supercharging if it is done properly. You would also need to upgrade your cooling system, your brakes and suspension set up. The list goes on, so do your homework well before taking the plunge.