After going through a bunch of exhausts, I went back to the factory STi axleback. I missed the boxer rumble though, so when a good deal came up on a Prodrive round tip axleback, I jumped on it. When I first installed the Prodrive, it was really quiet, only slightly louder than the factory axleback. I was confused enough to post about it in the main forum: https://www.i-club.com/forums/engine-power-ej20t-pre-2006-wrx-jdm-60/anyone-familar-prodrive-exhausts-196878/.

Now, after a couple of hundred miles, the exhaust is as loud as I remember, the boxer rumble and slight resonance is back. The exhaust had 5,000 miles on it when I bought it, so it wasn't new enough to require any type of break in and it's not old enough to be leaking.

So what happened? The only thing I can think of is that the ECM "learned" the new exhaust flow over the last couple of hundred miles and adjusted in a way that resulted in a louder exhaust note. Is this possible?

 

If you're running super rich, a vented BOV, or with no cats, you can burn the packing right out of your muffler.
It normally happens on n1 style mufflers, but I'm sure it's possible to burn the packing in other mufflers as well.

The packing is normally fiberglass or some composite material. If unburnt gas ignites in the muffler itself, it will slowly burn away the packing material if there is any.

If you have a vented BOV and no cats, you can actually backfire into the muffler but not hear it and that causes a small flame to come shooting out and literally burns the packing.
It also can happen if you run really rich.

 

^^^What he says...OR you have so much carbon build-up that it is rendering the muffling material useless (not sure if that is scientifically accurate).

There's a guy up here that just had a piece of pipe welded into the muffler to eliminate some of the muffler being in use...as such it is much louder.

 

The thing is, people who have had both the round tip and oval tip Prodrives say that they sound exactly the same. Now the exhaust sounds the same as the oval tip, but when I first put it on, it was really quiet. What I'm trying to say is that it sounds the way it is supposed to, but when I first put it on, it was real quiet.

I'm running catless, but I have a stage 2 flash so I don't think I'm running extra rich - there's no evidence of running rich on the exhaust, but I haven't checked the plugs.

Do the Prodrives run packing material to control the sound? I can see baffles inside the muffler, I was hoping that the sound was controlled that way instead of by material that will eventually blow out.

 

i think your learning to hear it better now you just had to get used to a totaly different note..............possible???? hmmmmm