I recently did an exhaust upgrade, from end to end and it was a risky experiment, but to stay on topic here, I started with an xForce CAT back 3-inch but retaining my HiTech dual tip mufflers on each side at the rear. Noise was harsh and loud at 92 dba, and not legal for the street, let alone the wife and neighbours!
So, first change was the front muffler, in the center section just behind the 3rd CAT. Went from this:
to this:
This is a Magnaflow 18x9x4 Oval with offset and allowed the fabricator to keep it tucked up into the original space. On that change alone, came back into the legal range at 87 dba. Was still too loud for me, but I wanted the flow.
The next change was to get rid of the HiTech dual tip mufflers. They were good for creating sound on a stock system, but doing what I wanted with a high flow system. Plus, with the higher exit gas temperatures due to the higher flow, I found the dual tip mufflers were melting the rear bar. The tips were now very close to touching the rear bar (poor xForce Y pipe alignment) and would touch and melt on WOT.
So, I grabbed the stock rear mufflers from the garage and put them back on. Sure it was quiet, but also restrictive and the raspiness was awful. I was like tin cans rattling in the rear every time I did a pull.
Then next change was to gut the stock rears and rebuild them as 2.5-inch straight thru with stainless steel and fibre glass packing. I was also able to have the alignment brought back into spec to match the xForce Y section that is retained on the car. They look like this:
These brought the sound pressure level into a nice place for me at 77 dba max on cold start, dropping to 60 dba at warm idle (nothing to see here officer!). On WOT, I reckon the level rises again to high 70's. Great for the family and neighbours, but with the high flow necessary to achieve the other developments.
If you want to see the full details, you can read it in my build thread, Project Veloci, starting at page 50:
http://forum.liberty.asn.au/viewtopic.php?f=10&t=12969&start=735#p323490 Not saying that what I have outlined here and in my build thread is the ideal for a 3.0R, but it is for my build.