Well I was having a bit of a read this morning on that very subject.
I read a few build threads, all on the CG13, one was running 1000cc bike carbs, aftermarket manifold and a Megajolt management running something in the region of 100bhp. Another was somewhat of a ghetto build running a low pressure turbo, T15 or something I think It may have been with stacked gaskets, That was making 120-130. The third build I read was another turbo build in a SR motor from France. This seemed to be built with a Galanza manifold a Decat mated to a CG flange, this was making 170PS, what ever that converts to in BHP.
To be honest I think I might just stick a B18 in there, i have considered a A+ turbo, but the costs compared to the gains is sort of putting me off. I will have long enough to think of a decent plan.