I'm adding a postscript to this thread, in case anyone wants to try to follow the path that I've started. One of the frustrating things about this messageboard is that sometimes folks won't report back what they've discovered as they try to do certain modifications, or make parts fit.
Unfortunately, I had a bit of bad luck trying to get my exhaust installed. The fabricator I initially contacted and who agreed to do the work, went out of business before I could get the parts together. (Perhaps in retrospect, that was a good thing!) I thought he was the only fabricator in the area, but after a bit of investigating, I found a full-service speed shop not too far from my home that doesn't advertise. He agreed to do the work, as well as anything else I can't do myself as I work towards supercharging my car. After a few minutes of speaking with him, I could tell he really knew his business, as well as caring for his customers' cars. (For example, he just purchased a new hydraulic lift with rubber guards on the arms to protect the pinch welds on cars.)
As it turns out, the GESI 3" ultra high output cats will not work with the Garageline X-pipe. There simply is not enough room against the undercarriage of the car. We briefly discussed the possibility of placing them at the front of the mid-pipes, but dismissed that location as being too far back and not having enough heat to operate them. He recommended finishing the install catless, and having me pick up the car and drive it a few miles to see how I felt about it. Some observations:
- The resonated Motordyne test pipes coupled with the factory muffler go far in moderating sound levels.
- I noticed beforehand that the factory cats passed quite a bit of raw fuel under certain conditions. By comparison, without the cats wasn't terribly different.
- He suggested that as time passed, the sound will get less as the insides of the pipes get coated with a layer of soot.
I drove it a few miles today, and quite honestly, there isn't a lot of difference now from stock. At normal speeds and engine load I can still carry on a quiet conversation with a passenger. At low RPMs and engine load there is a buzz/rumble through the floorboards and under the seat that wasn't there previously, but it passes as the RPMs climb. Plus, it revs noticeably easier. I'm going to have to retrain my clutching.
There is the hiss that others have reported with resonated test pipes as they fill with exhaust gas. Something to get used to, but not noticeable when driving with the windows up. There is a light but infrequent "burble" from the factory muffler when revving.
So, hopefully I won't have any major issues returning the cats to Vibrant. I'll also have to return the pricey Z1 metal gaskets I purchased for the test pipes. They did not fit well and leaked! The Motordyne test pipes come with a two-piece gasket with metal rings that sealed perfectly against the headers, and the Garageline system came with an extra pair that sealed perfectly between the test pipes and X-pipe.
If you want or need cats on a forced induction car, your only option is the full Fast Intentions system with mil-spec cats welded into the rear of their X-pipe. The Fast Intentions system will not mate up against any other system, so, if you don't like how theirs sounds, you are out of luck. I personally don't like how any aftermarket system sounds, but that's just me.
Now, hopefully, I can move beyond the exhaust to the next project: a stage 3 clutch and the RJM pedal!