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New Glass Pack Mufflers from Magnaflow

New Product: MagnaFlow Announces New Glass Pack Mufflers

There are a few phrases in the world of exhaust systems that automatically conjure up the “I want to go fast and I don’t care how loud” image. They are:

  • “straight pipe”
  • “cut-outs” and
  • “glass packs”

I’ve never thought of a glass pack as a particularly good thing. First of all, they’re notoriously cheap. They don’t do much in the way of “muffling” and the popular perception is that the fiberglass packed stuffing inside them (hence the name “glass pack”) is only going to burn-up and/or blow out.

New glass pack mufflers from Magnaflow

New glass pack mufflers from Magnaflow

However, when Magnaflow starts offering glass packs, you sort of have to pay attention.

Magnaflow’s newest offering is a glass pack muffler that’s available in a few sizes (smaller barrel = louder muffler), and they’re using something called “rockwool packing” that seems to be a durable sound deadening material that won’t burn out or blow out.

However, I’m just not a believer. First of all, glass packs are notorious for changing sound after a few hundred miles – I don’t know that these Magnaflows would be any different. There’s also the fact that Magnaflow’s Rockwool seems just as likely to burn up and blow out at some point as all the other glass packs before them. Check this out:

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While I’m not saying that these Magnalflow Glass Packs aren’t a decent product – I haven’t tested them so I just don’t know – I think they pros and cons break down like this:

  • Pro: Cheap
  • Con: Cheap
  • Pro: Loud
  • Con: Loud
  • Con: Probably going to burn out or blow out eventually, and then you’ll need to buy some more

If you want a cheap, loud muffler, this is just as good of an option as anything else (maybe better – Magnaflow’s stuff is usually very good). However, if you want a good muffler, a glass pack muffler seems like a stretch.


Designed for maximum performance, aluminized body, rockwool packaging for longevity and sound dampening, perforated core for straight through performance, precision robotic laser welding, flow bench tested and, as always, PROUDLY MADE IN THE USA. Read the full article…

8 Comments Post a comment
  1. jd
    Aug 13 2011

    how long do they usually last for a dodge 1500 V6 3.7L

  2. Scott
    Aug 26 2011

    I am wondering if the glasspack exhausts are the same design as other brands names for glasspack?

    Example, is Magnaflow, Thunder, Borla…etc the same design? I am not talking about size of the pipe diameter or length. The stuff inside the glasspack.

    • Jason
      Aug 30 2011

      Scott – The term “glasspack” is used pretty universally to mean a loud, unrestricted muffler, typically packed with fiberglass and little else. However, they are all a little different. Some exhaust manufacturers use packing/sound-deadening materials that last longer than others (more resistant to heat), so you want to follow the same general advice we have for all exhaust systems. Buy a name brand with a good warranty. 🙂

  3. morgan
    Mar 17 2012

    it’s kinda funny that people think of the round glass packs any differently than the rest of the magnaflow line of mufflers considering even there oval mufflers are the same thing shoved in a oval case, even the fart can’s are glasspacks just bigger

    in my view all glaspacks/magnaflows are very similar and are a deep natural engine sound which i personally like

    where as something like a thrush welded or a flow-master 40 changes the sound of most engines to a thumping echo of it’s self

    • Jason
      Mar 18 2012

      morgan – A fair point, but keep in mind the extra air space in an oval mufflers has a notable effect. Two mufflers with the exact same components but different shapes will sound differently.

      Still, I think you’re right – this is just a rebranded version of the same old muffler…

  4. Jason
    Mar 22 2012

    What kind of sound difference does the barrel length make?

  5. Nov 29 2012

    This is a great site to see a lot of videos about Magnaflow Mufflers. Thanks!

  6. Rust Never Sleeps
    Jun 14 2016

    In the realm of “glasspacks”, there are several factors to consider when choosing the “right one”.
    Some have a plain steel shell; some have aluminzed shells; some have stainless steel shells.
    Some have perforated cores; some have louvered cores.
    Some are directional; some are reversable.
    The stainless steel is more expensive, but has the longest service life.
    The louvered core is directional and offers more restriction(quieter) when mounted with the louver openings toward the engine. With the louvers facing rearward, there is less restriction, and there is a “swirling effect” applied to the exiting gasses.
    Different types of “fiberglass” have been used over the years, with the early ones packed with actual Ownes-Corning FIBERGLAS, which would burn or blow out after a few thousand miles. Later on, “long-strand” glass was (is still) used in the Walker/Dynomax/Thrush line of mufflers.
    Then comes the MagnaFlow Glasspack —
    Aluminized or Stainless Steel shell.
    Perforated core, with perforations designed to hold the packing in place.
    MagnaFlow Glasspacks are non-directional — they flow equally in either direction.
    The internal diameter (2″, for example) is maintained through the entire length of the muffler, which gives maximum flow for power AND fuel economy..
    I chose a pair of MagnaFlow 18134s for my 4.6 Liter Mercury V8.
    Aluminized, straight-through, perforated core, “rockwool” packing, and the unmistakable MagnaFlow sound.
    Ya gotta try real hard to keep your foot off the gas — the sound is intoxicating !!


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