agree with wasay
opening more exhaust flow is not key to get more power..it only get 1 or 2 hp back normally in cars which is blocked by stock tips
to get power u have to get fuel rich and then open the exhaust flow
as far as those cd70 and cg125 mods...its just there mind thing that they get more HP...which is not practically correct....
For yr bike you can get good performance exhaust ...contact any person dealing in sports bikes ...he is gona help you on this matter