get a 2t 50cc and whack a 70 kit on. the law will never notice. also there are some aftermarket exhausts available from leo vince, gianelli, etc that are higher performing but look stock.
'11 Honda Hornet '03 Gilera Stalker '03 MBK Stunt
'81 Honda NC50 Express '82 Puch Maxi S '70 Puch Maxi N