Before Mark Stewart at Kirk Racing Products caged our 350Z for its future life on track, we admittedly cut a fairly major corner: removing the sound deadening.
We skipped this miserable, time-consuming task to deliver the car on time. But we couldn’t paint our cage and take our car to the track until we finally got it done.
Sound What?
What’s sound deadening? It’s a material invented by Satan with the singular goal of adding difficulty to race car builds. At least, that’s what it feels like sometimes.
Sound deadening is present to some degree in every modern car, and its purpose is to damp noise and vibrations that would otherwise rattle anyone inside the cabin. What’s the difference between a Toyota and a Lexus? Besides the badge, the premium brand typically has some extra sound deadening that makes the ride feel more upscale.
Modern sound deadening is applied on the assembly line before a car is painted, and it’s basically baked on with special adhesive. Where it’s applied depends on the car and its needs, but you’ll usually find it on the floorboards, wheel wells and firewalls.
350Zs are particularly full of it, and our car also sported the stuff on its tunnel, firewall, inner fenders, spare tire well, and even under the speaker box on top of the fuel tank cavity.
Why Remove It?
Isn’t a quieter car a good thing? On the street, yes, but on track we have other priorities: weight and inflammability.
Sound deadening is really, really dense, and as a result it’s really, really heavy. It’s not uncommon to remove 20 to 50 pounds of it from a car, and that weight reduction costs nothing–well, except time.
Even though burn resistance standards exist for the materials found inside the car, sound deadening still represents 20 to 50 pounds of potentially flammable materials. “Most OE sound deadening is flammable,” explains Johnny Cichowski, professional racing consultant and owner of Nine Lives Racing, “and though it might sometimes be hard to light on fire, once it starts burning, it burns like an old tire.”
Bottom line: Sound deadening offers no benefits and a few major drawbacks for a race car, so we wanted it gone.
How Do You Remove It?
Ask five racers how to remove this stuff, and you’ll get five different answers and a fist fight. One thing is certain: It can’t just be peeled off unless you have months to spend with hammer and a chisel. Modern sound deadening sticks better than any substance we’ve ever seen, so you’ll need one of these tricks to get it off.
The first, heat, is the old standard. The process works like this: Grab a heat gun, point it at the sound deadening, and start scraping with a putty knife.
Expect horrible smells during the process. Afterward, the interior will be slathered with a greasy, glue-like substance. We’ve used this method many times, and while it works, it’s no fun and it’s not fast.
The second method, power tools, is a mistake. Just. Say. No.
Yes, you can grind off sound deadening with a wire wheel or flap disc, but after removing more than a few square inches, you’ll start clogging tools and breathing some truly horrible smoke. We’ve found that modern sound deadening tends to liquify once the tool reaches a certain rpm; at that point, you’re really just moving it around rather than removing it. Then there’s the damage left behind: You’ll end up with bare metal whether you like it or not.
The third method, dry ice, is a forum favorite and one we’ve used with mixed results. You use the negative-109-degree-Fahrenheit blocks to freeze the sound deadening until it’s rock solid. Banging it with a hammer will flex the metal enough to crack off the sound deadening material in big sheets. This works great in theory, but the reality is more complicated: Even with dry ice cubes, it’s very, very hard to get the material cold enough, and you’ll still end up doing plenty of scraping.
We were walking through all of these methods on the phone with Steve Eckerich, a longtime friend of GRM and a guy who’s built more than a few race cars, when he stopped us and mentioned method number four: liquid nitrogen.
You Can Buy That?
Liquid nitrogen, as Steve explains, is like magic sauce that makes sound deadening shed all by itself. Roughly the consistency of water, it sits at a temperature below negative 320 degrees Fahrenheit. In other words, it’s really, really good at making things cold.
“That’s cool,” we say before explaining that we are mere mortals who can’t access anything as badass as liquid nitrogen without breaking into the lab from “Stranger Things.”
“What are you talking about?” says Steve. “Buy a horse semen tank on eBay, then take it to your local welding shop and have it filled.”
That’s… a thing?
Yep. We fired up eBay, ordered some horse breeding gear from China for $190, and waited. Just to be safe we ordered a set of protective cryogenic gloves for $17, too, since liquid nitrogen can burn off fingers with instant frostbite. Neat!
A few days later, our liquid nitrogen dewar arrived, so we took it down to our local welding gas supply store. Sure enough, they filled it up for $40, making us the proud owners of a really, really dangerous flask of liquid.
On our way home, we stopped at a gas station to grab the last piece of our sound deadening removal puzzle: a $2.99 insulated coffee mug, which included a free cup of coffee.
We should clarify that while this stuff looks (and sounds) scary, the vapors aren’t dangerous. They do displace oxygen, though, so make sure you work in a well-ventilated area.
As a liquid, however, it’s extremely dangerous to bare skin, so cover yourself from head to toe in insulated waterproof materials.
Let’s Get to Work
Gloves? Check. Coffee mug? Check. Ten liters of the most dangerous thing we’d ever purchased without showing I.D.? Check. We donned our safety gear (waterproof leather boots, waterproof long pants, safety glasses and a face shield) and went to work.
And, well, the technique worked perfectly. After some initial trial and error, we settled into a groove: Pour a cup of coffee nitrogen into our insulated mug, slowly pour it over the patch of sound deadening we wanted to remove, then give it a soft whack with a rubber mallet if it didn’t pop off the car by itself.
With the help of an old putty knife, we were removing sound deadening in 8-square-inch chunks with barely any effort. For vertical sections, we duct-taped garbage bags onto the car to make little pockets that held the nitrogen in place. One bonus with this method: It leaves behind clean, unmolested sheet metal without a scratch on it, which will save us tons of time prepping the interior for paint.
After about 2 hours and the entire dewar of nitrogen, we’d successfully removed about 90% of our car’s sound deadening. We’ll have to tackle a few chunks here and there the old-fashioned way, but this process is by far the best we’ve found.
Does the nitrogen compromise the car’s metallurgy? After talking to a few experts, we concluded that the effects, if any, are negligible at best. After all, the sound deadening takes most of the thermal shock, and this method relies on the metal staying warmer and more flexible than what’s glued to it. The car is also a giant heat sink, meaning the metal is never truly supercooled.
Now that our 350Z is free of sound deadening, we can move on to the next step: finishing the interior so we can get back out on track. We’ll cover that in our next update.
Another method is to go to rally anarchy and enquire about the nitrogen death ray gun. You get a big dewar delivered, and then hook up the ray gun. When finished call up the gas supplier and they pick up the dewar. I've always wondered what would happen if you used a heat gun and then nailed the heated area with liquid nitrogen?
I'm not sure I want "horse semen tank" in my search history.
I pulled the sound deadening from the MG using an air chisel. Worked beautifully. But that was BMC-era insulation that was 40 years old at the time.
For those of you in colder climates, most places don't get "liquid nitrogen" cold but leaving a car out overnight when it's a decent amount below freezing will make sound deadening removal pretty easy the following morning by just whapping it with a rubber mallet, at least on 80s and 90s stuff.
what does it do to the wiring if hidden under the sound deadening ?
Did you weigh all the removed sound deadening?
The sound deadening is applied before wiring at the factory, so you won't find wiring under it.
I was weighing pieces at first, but since probably 1/3 of it turned into powder in the shop vac, I don't feel confident in my weights to publish those numbers. Instead, I'm periodically weighing the car as it comes together.
These need to end up in "Say What?"
"What’s sound deadening? It’s a material invented by Satan with the singular goal of adding difficulty to race car builds."
"Gloves? Check. Coffee mug? Check. Ten liters of the most dangerous thing we’d ever purchased without showing I.D.? Check. "
IIRC, back in high school, our science teacher demonstrated liquid nitrogen's power on a tennis ball. The frozen ball basically exploded once hit with a hammer.
Then, somehow, some dude's sneaker wound up in the liquid nitrogen. Yeah, it wasn't good for the shoe.
In reply to JoeyM :
Along with Keith Tanner's:
I'm not sure I want "horse semen tank" in my search history.
I still have some liquid nitrogen left in the dewar, too. If I get bored enough during this quarantine I'll start smashing random items around the shop.
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