I have the FI resonated cats with my stock IPL exhaust (G37) which is a true dual exhaust and assuming the same as the Nismo Z exhaust with slightly longer piping. A spot of rasp around 3K rpm initially and now that I've had them for a bit (two months maybe?) the rasp is gone and it sounds quite good from idle to redline. No drone but it is deep down low.
At cruising speeds it's dead silent. Can't hear it at steady throttle on the highway at all. The exhaust's volume is easy to control with the right foot!
My only issue with them is they do not have any sort of welded on tabs to attach to the car's OEM cat-converter bracket. As a result, there's a whole lot more vibration at idle. It disappears just above idle and is a non-issue from just off idle to redline.
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'13 Audi RS5 Misano w/mods-The Red Mist
'13 G37 IPL-SOLD
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