Another exhaust question: EF 3inch

[Henry4000]

Something I've been mulling over,
I had an EF GLI that ran a 3" mandrel system ifor a few days before I installed the blower and whilst it had the exhaust and no blower it was a real pig to drive. The auto changed much later on every shift and it sucked fuel terribly, sounded unique though! Once the blower was installed the car was in equilibriem and ran well, mostly.

I now have an EF XR6 in std form and (the supercharger lays in the shed till i rebuild the motor.) the std exhaust currently needs replacing and rather than get a shop to replace it I figure I could bolt the 3" system on since I already have it laying around. Why get a replacement that will only get replaced again??

The XR6 is manual so I'm interested if anyone knows how it might run and how fuel economy may look??? If anyone has a similar system I'd really like to hear your experiences.