Z has some junk inside the belly as well. It's a 50cc pipe after all... RS70 is a true 70cc exhaust, and there's no 70cc exhaust with a silencer in the belly.
Some years ago I modded 2 Leovince pipes, the Works and the Z. (removed the 'wall' from the belly)
While the Works performed much better than before, performance of the Z acually got worse. These pipes were designed with the silencing wall in place, so be warned.