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Presumably you are trying to compare the early S4 single outlet rear mufler with the twin outlet unit fitted to the 90 S4/GT and later GTS models?
If so an interesting comparison if anyone has tried both rear mufflers back to back on their specific example.
The only thing I would note is that the early S4's seem to have the larger mid resonator as fitted to the GTS's. The 90/91 S4 and GT's seem to have the smaller mid resonator and the GTS has the larger mid resonator [presumably same as the early S4's] so comparisons presumably would need to be conditioned.
In case you aren't aware, the GT and the GTS mufflers are identical.
I am not sure this is true. PET shows a -03 (928-111-097-03) rear muffler for the GT (M639) and Club Sport (M637). Switzerland (with stricter noise laws) got a different -04 twin-outlet muffler (known affectionately as the "Humorless Swiss" version).
S4s through '89 got the single-pipe -01 version, then the -04 "Swiss" version. The GTS also got the -04 "Swiss" version. That's what our GTS still has, and I can report that it is very quiet-- quieter than our S4 was with the -01, and much quieter than the -03 GT muffler.
Find the -03 GT muffler if you can, they are pretty rare.
I was going on the basis of my experience. I traded a RMB to a neighbor for a nearly new GT muffler. The part number on that muffler was identical to the part number on my '94 GTS muffler.
Could be wrong, but I'm sure the original Houston owner of the GTS had not changed the muffler, as i had every service record after 22K miles.
It's relative to the person. You've heard Nicole's 91, that's what yours will sound like with it.
I have had a 928 International RMB for years. It gives the car a somewhat aggressive growl.
But I'm seriously thinking of going back to the stock muffler - After driving electric cars as daily drivers for 5 years, I find the RMB sound level rather annoying these days.
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