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SO-CAL Speed Shop Recesses A Model A Firewall - Time For RecessFrom the December, 2010 issue of Rod & Custom By Kev Elliot Photography by Kev Elliot
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If you want to fit a small-block Chevy-or most any OHV V-8-in a Model A, and retain the stock frame and wheelbase, something's going to have to give; there simply isn't enough room between the radiator and the firewall where a four-cylinder motor once lived to fit a V-8, despite the fact that an eight is only four-cylinders long. The solution has always been to recess the firewall. There are a number of ways this can be done, from using a section of a wheelbarrow, to purchasing ready-made recessed firewall sheetmetal. On a '30-31 Model A we've even seen the firewall removed and re-installed backward. With the body on the chassis,... With the body on the chassis, the motor mounted, and the headers, valve covers, and distributor in place, Richie Nogueira cut a section from the firewall. While not as large a "hole" as would be required, it's better to sneak up on the final size then remove too much too soon. A couple of lengths of 6-inch-wide aluminum were then bent up as templates to get an idea of the recess required. These templates were also useful for determining that the valve covers could be removed with the angled sections of the recess in this position. One of the current projects underway at SO-CAL Speed Shop is a '31 Model A pickup, with a small-block Chevy and stock chassis. These early pickups are not exactly roomy on the inside, and any reduction in interior space will always be undesirable, so the decision was made to make the recess as small as possible, retaining maximum legroom and allowing space behind the dash for an air conditioning evaporator. We followed along as SO-CAL Speed Shop's Richie Nogueira fabricated a recess for the firewall from 16-gauge steel, making it appear as "stock" as possible. If you're planning a similar sheetmetal adventure yourself, make sure you have the valve covers and distributor you intend on using, as not only will you need them for clearance, but you'll also want to be sure you're able to remove them once the job's finished!  With some sections of stiff...  With some sections of stiff poster board taped together, the templates were used to determine the size of the pattern, and where any bends should be. Scissors were used to score the card to make bending it easier.  Voilá! Looks like it'll work....  Voilá! Looks like it'll work. And yes, we know one side of the "hole" has been trimmed farther out than the other. At this stage Nogueira was merely mocking it up to check clearances and appearance.  Before the template/pattern...  Before the template/pattern assembly could be trial fitted in the cowl, Nogueira drilled them then used Cleco fasteners to hold them together, as the clamps used up to now would have to be removed.  Bent to shape and clamped...  Bent to shape and clamped to the templates, the recess is beginning to form. Nogueira's initial plan was to bend the top corners as shown, requiring only one weld to join it to the top section. However, bending this section would be impossible to do in the brake, plus it would require two further triangular sections be fabricated and welded into the outside flange. Nogueira decided to fabricate separate filler sections from a single piece for each side.  Swage lines formed by bead...  Swage lines formed by bead rollers are one thing, but making them look like factory pressings requires a little work and a lot of skill. The area where they intersect was worked to "round" the corners, as were the ends of each swage.  Looks a little different to...  Looks a little different to how it did straight from the bead roller, huh? Note how a compass was used to scribe a radius at the end of each swage, which was then worked to follow this line.  Once happy with the pattern,...  Once happy with the pattern, it was removed from the templates, laid out flat again, and its perimeter replicated in 16-gauge steel. Nogueira decided to add a swage line for character.  Nogueira used various tools,...  Nogueira used various tools, mostly homemade, to work the swage lines. Don't be afraid to make a tool if it'll do the job. The hard plastic tools were made by Nogueira over a decade ago, while the little T-bar was particularly neat. Note the panel was worked from both sides, depending on what needed doing.  Once cut to size, a wooden...  Once cut to size, a wooden mallet was used to form the outer flange, hammered over a piece of round steel stock welded to a flat plate clamped in a vise.  The panel was bent in the...  The panel was bent in the brake, but rather than sharp bends, a radius was desired. A length of tubing welded to flat stock was clamped in place of the usual fingers on the brake to achieve this.  After each corner piece was...  After each corner piece was tacked, a shrinker/stretcher was used to bring the top flange into perfect alignment.  With the radiused bends formed,...  With the radiused bends formed, the panel was held upright on the bench using a pair of magnets at each side, in order for the top corners to be fabricated. With a 90-degree radiused bend formed and the corner worked in to a curve, Nogueira held the corner panel in place and scribed cut lines onto it.  One corner piece tacked in...  One corner piece tacked in place, and one to go. Note the relief cut in the corner of the flange.  Here the second corner is...  Here the second corner is tacked in place. Note the tight tolerances between each of the sections, essential when TIG welding.  After a trial fit, the firewall...  After a trial fit, the firewall was trimmed a little more and the corners radiused using a drum sander in an air grinder.  Another trial fit showed everything...  Another trial fit showed everything was good. Note the MSD Pro-Billet distributor, which will be used is now in place. While we said to make sure all your components are in place before starting such a job, the MSD piece is smaller in diameter and shorter than the stocker used for mock-up, so no clearance problems were anticipated.  It was checked at the beginning,...  It was checked at the beginning, but doesn't hurt to check again before final welding. The distributor can be removed and replaced with the motor in place thanks to the height of the recess.  Sharp-eyed readers will have...  Sharp-eyed readers will have noticed the firewall was held in place with Clecos at the start, and here's why; it was way easier to complete the final welding with the firewall laid on the bench than to attempt it while in the car. The gaps at the lower corners were also addressed at this time, with filler pieces welded in.  Here's the view inside the...  Here's the view inside the truck once a removable trans tunnel had been fabricated. As you can see, there's ample legroom inside the cab even with the recessed firewall.  The finished firewall, with...  The finished firewall, with a recess that looks almost "factory" doesn't eliminate too much interior room, and still leaves enough space for the A/C evaporator behind the dash. The two small vertical swage lines remaining on the upper portion of the firewall were cut out and welded smooth.
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