[RestoCreations]

Glasspack mufflers are glasspack mufflers. The only way that they will be quieter is if the Internal diameter of the muffler is smaller. it will be more restrictive, but you can also fit more packing/sound dampening material around the muffler. Our cars use very short muffler sections, which is the majority of the problem. If you could find someone that would make a 2" or 2-1/4" internal diameter muffler, then i think it would help dramatically.
On a previous car, i custom made a set of 2-1/4" internal diameter chambered mufflers. They worked and they shut the exhaust up a good bit, but it was a huge hassle and a ton of work. Overall i had a 5db decrease across the rpm range until about 65mph where the wind noise took over. I lost about 8rwhp total. However, I could not feel the loss and was more than happy to sacrifice a few hp to quiet the pipes down. I have used mufflers from some of the companies mentioned and i can tell you there is no Decibel difference or hp difference. If you are swapping one brand of 2-1/2 or 3" glasspacks for another brand, there really isnt a difference as far as sound levels are concerned. All are chambered exhaust with small louvers and wrapped with fiberglass. I wish someone would make a glasspack with a 2" or 2-1/4" ID muffler with a smooth transition into from pipe to muffler. Yes, you will sacrifice a little hp, but I am willing to give up 10-15 RWHP, probably even 20 in order to keep more of my hearing.
-One more point. I have heard a car in person with the spiral inserts and they do not sound good unless you like a very metallic sound to your exhaust. It was far too much for me. I have heard that the spiral cones will drop the noise a db or two, but that is not enough for me to bother with the effort of installing them. I have also heard that the Car Chemistry tip inserts work, but that was only from one source. Car chemistry used to offer a full length insert, but i do not see it on their website anymore.

You would really think with all of the complaints that someone would make a better muffler. The small inserts, regardless of brand, seem pricey to me for what they are.