I would bet you have lost some flow with this set up, maybe even a few hp and some added a little extra boost from the new restrictions. The exits of the Corsa mufflers have been restricted to a much smaller pipe, addition of more bends and out the centre pipes. Would of been a much more efficient system if you cut the centre tips and had them welded in place for looks only, and just ran the Corsa muffler straight dumped like the factory dumps.
Bad idea if your looking for performance