Do glasspack mufflers "wear out"?

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Put a turbo muffler on it. We run the generic magnaflow on our cars, they do a good job of keeping the noise down.

You could put a used, or cheap new, resonator in the pipe.  Or put more pipe on and run it over the axle and out behind the tire.  It is amazing what a few bends in the pipe will do.

In our Mustang the exhaust exits out the passenger side in front of the rear tire.  It is still pretty loud coming out that side.  I just put ear plugs in.  You can still hear all the noises, but you are not deaf at the end of the stint.

"WHAT?!? SPEAK UP!!"

We run a glasspack on the ZomBee. I don't think it ever wore out. I think the rest of the world got quieter.

If you've hung the glasspack directly of of the header, it could have worn out due to the excessive heat, especially from prolonged track time. You gotta figure that the racing is always going to overstress parts designed for the street. I'd just look to Craigslist for a used FlowMaster. A muffler like that is designed to attenuate sound, especially tones that are considered unpleasant. It's also a lot less likely to crush when one of your drivers manages to run over the larger debris falling off of the cars in front of you.

Be sure to support the weight of the muffler with hangers and not the header.

You could also swap in a Mazda Rotary, they're not too loud.
In fact, "Piston engine goes 'Boing, boing, boing, boing boing...' but the Mazda engine goes 'Hmmmmmmmmmmmmmm...'"

Our engines melt and kill glass pack mufflers in short order. 

Rotary engine exhaust is just toooo damn hot.   After reading about Mazda's solution on their racing engines, we decided to give it a shot:  the Lava Rock Muffler!

Google it and you'll get the idea.

We took a melted glass pack (a chambered design won't work), cut the casing, peeled it back, and stuffed it tight and  full of lava rocks from Home Depot Racing and Development (in the lanscaping section ).   When we were done, we welded the surgery wound closed and installed the muffler.   

You have to remove the melted nastiness inside the muffler to make room for the lava rocks, so wear some gloves or you'll be itching like no tomorrow.

Was it hella LeMony?   YES!  Its a shame that no one got to appreciate the genius of it.

Was it loud?  Hell yes.   
Was it quiteter than a glass pack?  Yes, I think it was
Did it sound good?   Well of course, rotaries have the sweetest song.    Your favorite song always sounds better when you turn it up just a bit.