i.ve done this with a Handmade Works , but in that exhaust there was another pipe in de middle , like a catalizer , I took the parts out en tested is , it onhly made more noise but absolutely no powerincrease , it was worse....
Leovince exhausts are calculated to do it's job when it is in tact , when you take everything out the whole exhaust is not working as it should be.. the volume get's to big.
but in your exhaust there was no small pipe inside? that could explain why it worked with your exhaust en not mine , altough i sawed open several LV HM exhausts en in those pipes where also these catalizer like pipes. the old Handmade (first type)however has only the perforated metal sheed inside , the outside diameter was also a lot smaller.
[EDIT] , I remember now , the HM has these pipes inside , ZX has no pipe , there is the clue to wy you didn't discover a pipe inside while i did
i hope this adds something to this topic , that only ZX has no pipe ,maybe the S are also without pipe.