Hello and welcome to the forum. Unfortunately, there isn't a lot of hop up parts for the Bis, if at all. Several attempts have been made to convert the Bis with a bike engine, but I have yet to see one legally on the road. Many, if not all of the bike conversion projects, have ended up unfinished, and sold as spares or repair. With regards to adding a turbo, I have to see a Bis with one installed.
I am not an expert, but the only option that comes to mind is, perhaps skimming the head, port and polish and reboring the pistons for more umph.