It’s often the stuff you can’t see that makes the difference between a good and a great street rod. When you’re restoring or building a project vehicle, it’s common to focus most of your attention on the obvious items, such as the engine, bodywork and upholstery. What about those areas beneath and behind them, though? Without sufficient insulation for heat and sound, your rod could end up being a hot and noisy ride. That might be kind of fun for a short run, but not on a longer cruise.
As a case in point, let me share a personal experience. In a previous life I worked for a certain well-known Texas chicken farmer (now known for his racing exploits and sports cars), who decided to reintroduce the Cobra that he had created back in the Sixties.
When our factory mule was put together rather hurriedly as a display vehicle, a few key items were left out, such as barrier materials (insulation) in the fiberglass cockpit, and a rubber grommet on the steering column where the shaft passed through the firewall. So when that 427 big-block V-8 came up to operating temperature, a blast of hot air would hit the nether regions of the driver. While we jokingly referred to this feature as the “Shelby nut roaster,” it made for a really unpleasant driving experience (not to mention lowering the fertility rates of male drivers).
Personal comfort aside, high levels of noise and heat can also interfere with your reaction time and driving ability. On the other hand, with good insulation, your air conditioner can operate more efficiently (thus reducing fuel consumption and the risk of radiator boil-over). Also, your audio system should have better fidelity.
To see what’s involved in reducing sound and heat in a street rod, we sought out some expert assistance from Tim Cox of Quiet Ride Solutions who recently insulated a 1928 Ford Phaeton. Even though this particular vehicle is rather rare, the principles of sound and heat shielding apply to just about any type of rod, whether a steel original or a fiberglass reproduction.
Drawing on Cox’s advice and experience, we’ll address the noise aspect first. Note that sound can emanate from a least two different sources on a car: via a solid material (the frame and body panels) and through the air (such as from the exhaust pipes, and somewhat surprisingly, the air intake as well).
Lowering airborne noise might require toning down that noisemaker under the hood, which is simply not an option on a muscled-up rod (we don’t want to spoil all the fun here!). However, one option for an enclosed car (coupe or sedan) is to check the rubber stripping on the windows. If you spot any big cracks or missing chunks, install new rubber (Steele Rubber is a good source for this type of product). If the rubber looks dry but is otherwise intact, apply some vasoline to make it more compliant for a better seal. In addition, inspect the floorboard and firewall for any unnecessary openings (which also might help with an open-top roadster). Those can be filled with spray-on foam (the type typically used for filling holes and cracks in home-remodeling projects).
As for minimizing vibration-borne noise, the basic approach is similar to placing your hand on the skin of a drum. Flat areas of your street rod’s sheetmetal (or fiberglass) produce the most sound, so those need the most attention, but the entire cabin area should be insulated wherever possible.
Installing Dynamat, a material composed of rubber and aspalt, is the rough equivalent of placing your hand on the drumming motion of your rod’s interior body panels. Quiet Ride Solutions, one of the country’s largest distributors of Dynamat, starts an insulation project by laying down intermittent strips of this self-adhesive material.
Why not use just one big sheet? Keeping the cost down is one reason, and Cox says those individual strips work just as well. Why so? Imagine dropping a stone on the surface of the water, which forms ripples. Those waves of water provide a visual analogy to sound waves, and the Dynamat strips act as breakwaters to attenuate the motion. In addition, from an installation standpoint, laying down small strips easier in tight corners or other hard-to-read areas of a street rod.
Next goes on a layer of Quality Heat Shield, dense padding bonded to a reinforced layer of aluminum foil. It’s important that the foil be placed on top (instead of against the body panels) for several reasons. It not only serves as a skin to protect the padding, but also creates an air pocket, similar to a double-pane thermal window. It’s that layer of air that provides the insulation (sound travels more easily through solids).
As just one example, Cox recalls a hot-rodded ‘64 Chevelle that he insulated. Prior to adding the materials, at 60 mph the sound level was 100 db (equivalent to that of an unbridled jackhammer, he says), but afterward, it dropped to 80 db. Ditto for the levels at idle (80 and 60 db, before and after). That’s a huge difference, especially when you consider that decibels are measured on a logarithmic scale, so this decrease represents approximately 50 percent reduction in sound!
As for reducing temperature, the foil also helps to reflect back heat emanating from the engine and exhaust system. This material acts a fire retardant, and reflects back 97 percent of infrared energy, Quiet Ride claims, resulting in a temperature drop of as much as 30 degrees. As already noted, this reduction can benefit both the passengers and the engine.
It’s fairly easy to put in the materials, and Quiet Ride offers a wide range of pre-cut kits for cars, trucks, RVs and other projects. A universal package that you can custom fit is available as well.
It’s important to make sure the materials form a consistent barrier or envelope that’s sealed with foil tape at the seams, and is glued down securely. Otherwise a small opening might create your very own “nut roaster” as well!
Quiet Ride Solutions
6507 Pacific Avenue, Ste. 334
Stockton, CA 95207
Quite Ride’s offers both universal (shown here) and factory pre-cut kits. Each includes include Dynamat strips, Quality Heat Shield, spray-on adhesive and foil tape. If you have a custom buildup project that requires the universal kit, electric scissors should make the cutting job much easier.
This closeup shows the Quality Heat Shield’s reinforced aluminum foil and dense fabric padding. The foil side will be installed facing up.
Prior to installation, lay out the pre-cut pieces of Dynamat throughout the interior to get an idea of where they’ll fit. The blue tape covers the self-adhesive side, so these strips will be turned over later on and pressed in place after determining their correct location.
Even smaller areas such as this footwell and door panel should be insulated with Dynamat.
The blue backing tape peels back to expose the self-adhesive side of the Dynamat.
Use a roller to press the Dynamat strips in place, so they bond tightly with the sheetmetal.
Dry-fit the Quality Heat Shield in place to make sure the piece you’ve cut (or selected from the factory kit) properly covers its install location.
Spray adhesive on the underside of the padding. A double application on the edges is a good idea to ensure a tight bond.
After adhesive is applied to both surfaces, lay the Quality Heat shield on the Dynamat strips.
The insulation can be fitted into partially enclosed areas by folding it.
Here’s how the Quality Heat Shield looks once it’s installed. Seems almost a shame to cover it up with carpeting and upholstery.
Be sure to apply foil tape to all seams.
This decibel meter showed an immediate drop in sound level after installing just the insulation. Once the interior is re-installed, the noise level should be reduced even more.