Everything You Should Know About Glasspack Mufflers

Everything You Should Know About Glasspack Mufflers

Last Updated December 13, 2021 | Meghan Drummond
Contents

When it comes to muffler options, one of the most popular is a “glasspack” muffler. From the outside, these look like straight-through tubes, and they offer many of the same benefits as straight piping. But there are some key differences that contribute to glasspacks’ ongoing popularity.

diagram showing flow of exhaust and sound through glasspack muffler

What Is a Glasspack?

A glasspack muffler features a perforated exhaust pipe that’s surrounded by fiberglass (or sometimes steel wool) and then wrapped in a steel or aluminum shell. This is different from a straight pipe, which doesn’t have any sound-absorbing insulation.

Basically, a glasspack is a straight pipe, but with a layer of absorption that modifies the sound. The straight design improves exhaust flow and reduces backpressure for better performance. But the sound dampening works to create a better, rumbling sound that’s preferable to the screech of a straight pipe.

The first glasspacks were created in 1968 by Cherry Bomb. That’s why they’re still sometimes called “Cherry Bomb” mufflers.

Though many companies make glasspacks now, bright powder-coated finishes are still a staple of the style.

Are Glasspacks Loud?

There’s a lot of variance in how loud glasspacks are. But on the whole, yes, glasspacks are one of the louder types of mufflers you can have. The only things louder than glasspacks are straight pipes and muffler deletes.

The type of packing and the quality will impact how loud your glasspacks are. Many manufacturers now use a quieter, more durable stainless steel mesh instead of fiberglass. Stainless mesh is more expensive, but it’s great for people who want the performance benefits of glasspacks without the loud noise.

The length of the glasspack also impacts the volume. A longer glasspack will be quieter, a shorter one will be louder. That’s because a long glasspack has more time to dissipate sound.

Why Are Glasspacks Popular?

Glasspacks have a few key benefits that have contributed to their enduring popularity. Perhaps the biggest is simply that people like the way they sound. But here are some other tangible pros for glasspacks.

Flowtech's Red Hot and Purple Hornies glasspack mufflers

Cost

There’s not a lot of technology that goes into making a glasspack. As a result, they tend to be pretty inexpensive. Flowtech’s Red Hots and Purple Hornies are great examples of affordable tubular glasspacks. Both of these options are available for under $50, and can usually be self-installed. Other glasspacks can cost more, but they tend to be among the least costly muffler options.

Volume

Glasspacks can be loud. They sound aggressive and can change a stock exhaust into a rumbling one with very little work. Cat-backs and axle-backs are better, but they’re more expensive and require a more involved install.

For people who want a loud, inexpensive exhaust, glasspacks are a go-to.

Horsepower

A glasspack is basically a straight-through. It’s much less restrictive than a factory muffler, and it reduces backpressure to free up horsepower. Depending on how restrictive your factory muffler is, you could see gains as high as 20 horsepower from adding a glasspack.

Downsides to Glasspacks

No modification is totally free of downsides, and glasspacks are no exception. These are the biggest cons to this muffler style.

Blow Out

The major downside to glasspacks is that the packing doesn’t last forever. Over time, the fiberglass packing will degrade and “blow out.” This isn’t a great name, because you might not see anything blow out of your muffler. But, if you could look on the inside, all you’d find would be an empty can.

As the fiberglass wears down, the sound quality may also get worse.

High-quality glasspacks have better packing and will last much longer before breaking down.

Legal Issues

Most states have limits on how loud your exhaust can be. While that may seem unfair, imagine how annoyed you’d be if someone woke you up in the middle of some much-needed sleep.

If you live in a neighborhood, around other people, a little logic will go a long way. But if you’re modifying your exhaust, you should know the laws and regulations in your area. In some states like New York, a loud exhaust could cost you a grand or more.

If you’re not sure how loud your exhaust is, download a decibel reader to your phone and get some measurements. Remember, your hearing is also important, and being exposed to loud noise for too long can cause permanent hearing damage.

Installing a glasspack muffler on a Mustang

Volume

If you’re used to stock mufflers, glasspacks are going to be a big change all at once. A lot of owners are surprised to find that the sound inside their cabin is too loud for music or conversation.

It may be a good idea to try out a milder muffler at first and then try glasspacks if that’s still not loud enough for you. Or, check out a local car show or meetup. Ask about other people’s exhausts, or take a ride with a friend and see how their exhaust sounds at a variety of speeds.

Drone

Interior drone is a serious problem with exhaust modifications. That’s especially true of anything that promises to be loud and deliver horsepower at a low price. Many glasspacks struggle with drone, which can be obnoxious at highway speeds.

Glasspack Pros and Cons

Glasspack Muffler Pros and Cons
ProsCons
Low Cost Fiberglass Can Blow Out
Adds Horsepower Potential Legal Issues
Loud Volume Loud Volume

When you add it all up, it’s easy to understand why glasspacks have enjoyed such popularity. The cost-benefit analysis definitely leans in its favor. But if you’re looking for something that’s going to last longer and give you more volume control, there are some alternatives to consider.

Glasspack Alternatives

Some manufacturers have come up with glasspack alternatives. These mufflers aim to replicate the sound and performance of a glasspack without the blowout.

Flowmaster’s Outlaw tubular mufflers use sound attenuation rings instead of any kind of packing.

Interior view of an outlaw muffler with attenuation rings

Borla’s Sportsman racing mufflers are packed with continuous-filament fiber material. Coupled with a stainless steel inner core that’s resistant to the acid byproducts of exhaust gases, the packing shouldn’t break down or blow out.

Either of these would offer the glasspack sound, but with a much longer lifespan.

If you’re really interested in a better sound experience, you may want to look into axle-back or cat-back kits. These are a little more expensive, but you’ll get more improvement in sound and performance.

Glasspacks are inexpensive mufflers that deliver performance gains and a loud sound. If you’re looking for a fun modification, they’re definitely near the top of the list. For a longer-lasting option, or one for your daily driver, a different muffler may be a better fit.

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About the Author

Meghan is a Classic Mustang geek with a soft spot for four-eyed Foxes. She has over 300 in-depth articles to her credit that have been cited by some of the top news sites in the US. Read full bio →

Sources: Cherry Bomb Glasspack Mufflers, Cherry Bomb | Glasspack Mufflers 101: Sound, Power Gain, and Are They Legal?, Car Performance Boss | Frequently Asked Questions, Borla Exhaust

This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about CJ's editorial standards and guidelines.

Everything You Should Know About Glasspack Mufflers

Glasspack mufflers are a polarizing topic. Whether you love them or hate them, here’s what you should know about this popular exhaust modification. There are some serious pros (and cons) to these mufflers.