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1970 Chevy Nova Gets A Smooth Firewall - Great Walls Of Fire!Smoothing Out That Lumpy Firewall Can Give Your Engine Bay Some High-End Flair. Best Of All, With Some Careful Planning, It's Easy To Do. From the May, 2009 issue of Popular Hot Rodding By Stephen Kim Photography by Precision Coachworks, Scott Killeen
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Think of it as cellulite removal for sheetmetal. At its core, a firewall is nothing more than a barrier that prevents a car's occupants from getting too toasty. It's been known to seal the cabin off from stinky fumes and toxic fluids on occasion as well. Given its utilitarian nature, the landscape of a firewall is characterized by undulating topography and unsightly holes. There's nothing pretty about it. While that's fine for a production car, spending a little bit of time smoothing that sucker out is a great way to score a ton of style points with your project car. Best of all, anyone with some basic welding skills can pull it off. All it takes is some advanced planning. For some helpful pointers, we watched closely as the crew at Precision Coachworks reprofiled the firewall on Air Ride Technologies' '70 Nova. For those who may be hesitant to go crazy with a cutoff wheel, smoothing out a firewall is a low-risk, high-reward endeavor that doesn't require the skill of an expert bodyman. "I wouldn't put a high degree of difficulty on a project like this because we're talking about a relatively small area of the car," explains John Hemmer of Precision Coachworks. "The firewall is much stronger than the fenders or quarter-panels, so it's harder to inadvertently warp. Plus, since the motor will cover most of the area you're working on, even if it isn't perfect and there are a few flaws, it's no big deal and it will still look a lot better than stock. Even if you aren't completely comfortable doing bodywork, a project like this is very feasible." That said, smoothing a firewall requires a fair amount of advanced planning, and many of the procedures outlined in this story are specific to Air Ride's project Supernova. For obvious reasons, it's best to plan on tackling a job like this while the motor is out of the car and before the body has been primered. More importantly, the holes that can be plugged and the areas that can be flattened depend on exactly how the car is configured. For instance, different types of steering columns, pedal assemblies, shifter locations, master cylinders, and A/C systems all impact where the cutting and welding will take place. Likewise, many of the holes in a firewall were punched by the factory simply to run wires through, so carefully routing your wiring to one or two central points will allow plugging up more holes and yield a much cleaner finished product. By taking time to plan ahead, you'll be able to turn lots of heads on cruise night once your project is complete.  When Air Ride was planning...  When Air Ride was planning their Nova, one of the first things they wanted from Precision Coachworks was a smoothed firewall. We can't emphasize enough the importance of putting your project plan in writing with a build wish list and a project rendering. It will save you the cost of doing many things twice. Smoothing the firewall is one of those things that must be plugged in during the planning stage.  After sandblasting the body,...  After sandblasting the body, the Nova was propped up on a rotisserie to begin the firewall smoothing process. Although the media blasting removes paint, grease, and debris from the metal, the factory seam sealer on the Nova's rust-free body required further attention. Cleaning out the sealer with a wire brush and a cordless drill makes warping the firewall with excessive heat buildup next to impossible. Rust has already eaten through this seam in many cars, so this step may not be necessary depending on the condition of your body.  Before any cutting and welding...  Before any cutting and welding of the firewall starts, it's imperative to plan which holes will be plugged, and which will be left alone. This depends on several factors, such as the type of pedal linkages, steering column, and master cylinder that will be used, as well as how the wiring will be routed through the firewall. Then it's simply a matter of cutting out plugs from 16-gauge steel and MIG-welding them into position. John suggests first creating a template by holding a piece of cardboard up to the engine side of the firewall, then tracing the hole from the interior side of the firewall.  Since Supernova is equipped...  Since Supernova is equipped with a compact aftermarket steering column, the large hole for the factory column was plugged up and recut. With aftermarket brakes, the holes on the far right for the factory parking brake assembly were not necessary either. After plugging up the holes, the welds were ground down with an angle grinder. Either an air or an electric grinder will suffice, and John recommends using a 3-inch, 36-grit wheel to limit heat buildup and prevent warping the metal.  Installation of a Vintage...  Installation of a Vintage Air A/C system enabled flattening out the metal surrounding the factory heater box area. This required substantially enlarging the factory hole before plugging it up with a plate. While the factory hole is relatively small, it is surrounded by several contours. Precision Coachworks' Shane Wagner trimmed the area around the factory hole with snips and a die grinder until reaching the flat portions of the firewall. At this point, the body was placed on a custom jig, but this procedure can be performed just as easily on jackstands.  To prevent warping the metal,...  To prevent warping the metal, the tack welds were spaced roughly 3/4-inch apart from each other. On each side of the plate, welding from the center outward helps keep the panel square in the hole. Likewise, hitting the welds with an air nozzle from time to time ensures the metal won't overheat.  While it's by no means a necessary...  While it's by no means a necessary step, the heater box block-off plate was put through a bead roller to emulate the look of a factory heater-delete car. Not only does it look slick, the bead rolling process gives the metal additional strength. To achieve the look, Kurt Blackgrove held a template up to the plate to determine where and how much of the metal to roll. He then drew around it with a marker and formed the metal into shape.  With the heater box hole plugged...  With the heater box hole plugged shut, Shane ground down the welds using long strokes to avoid excessive heat buildup. At this point, the welds, block-off plate, and firewall are essentially one solid piece. Getting it just right eliminates the need for body filler. Simply grinding and blocking the metal will result in a surface that's flat enough to paint.  To make room for the column-shifted...  To make room for the column-shifted automatic, the factory cut an enormous oblong-shaped hole into the Nova's firewall. Since Supernova was fitted with a 4L65E overdrive shifted from atop the trans tunnel, the factory hole was plugged. Moreover, unsightly factory spot welds were plugged and ground flat. Note the location of the stock gas pedal hole in the far left.  Having ditched the factory...  Having ditched the factory gas pedal assembly for a custom-built unit, the stock hole was eliminated. For obvious reasons, this hole can't be closed off if the factory pedal assembly is retained.  Upon completing all welding...  Upon completing all welding work, any remaining high spots must be knocked down with an angle grinder. The goal is to use as thin a coat of body filler as possible. For a super clean end product, Precision Coachworks ran all the wiring through the inner fenders, which enabled plugging several extra holes in the firewall. Likewise, the hole for the body access mount (bottom right), a passage that makes it easier to detach the body from the subframe, was plugged as well.  It's possible to jump right...  It's possible to jump right to block sanding and priming after the metalwork is complete, but John says that adding body filler yields a more polished end product. A thin 1/8-inch-thick skim coat of filler is all that is necessary. Just about any type of mud will work fine, but John prefers marine-grade fillers since they're less likely to develop pinholes.  The irregular surface of the...  The irregular surface of the firewall can make block-sanding difficult, so John recommends using a rigid foam block that is flexible enough to conform to the metal's contours. Shane started with 180-grit paper, then hit the surface again with 240-grit, followed by 400-grit.  Having already achieved a...  Having already achieved a very flat firewall surface that didn't need much filler, John opted to spray it with a urethane (2k) primer. For firewall surfaces that aren't as flat and require more fill, an epoxy or polyester primer is preferable.  The final step before painting...  The final step before painting is applying a dab of seam sealer around the firewall. John prefers 3M sealers for their durability and quick curing times.  Not a fan of shiny firewalls,...  Not a fan of shiny firewalls, Precision Coachworks' finish is a secret brew of semi-gloss black and an undisclosed textured ingredient (we prefer Sherwin-Williams Matte Clear, PN CC947, $57.05 per quart). Regardless of the ingredients, it looks a heck of a lot better than stock. Obviously, the particular color you choose to paint your firewall is strictly a matter of personal preference.  A smoothed firewall is just...  A smoothed firewall is just one ingredient making up the impressive whole of the finished car. This is the type of detail that can push a very nice-yet ordinary-car over the edge into trophy-winning territory. If you've ever wanted to get your hands dirty with custom bodywork, smoothing the firewall is a great place to start that gives the beginner a lot of latitude in the skill department.
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