Fabricating a Recessed Firewall – Valley Of Fire

By Ron Covell
Photography by Tim Bernsau

Not quite, but the firewall on this year’s Road Tour coupe now accommodates our Ford Coyote hi-po V-8

In this installment of the 2012 AMSOIL/STREET RODDER Road Tour ’40, Troy Ladd and his crew at Hollywood Hot Rods are making a recessed firewall. You might wonder why the firewall needed modification at all. When Bob Drake designed his “new” ’40 Ford coupe, he decided to offer both a stock firewall and an optional Hot Rod 5-1/2-inch recessed firewall that can accommodate a wide range of both small- and big-block V-8 engines. The body we’re using already had the Hot Rod firewall.

Two issues drove the firewall modification. First, the Ford Coyote V-8 with dual overhead camshafts is an extremely wide engine, actually wider than an early Chrysler Hemi. (The Ford Racing 5.0L Mustang Boss 302 crate engine takes the Ti-VCT 5.0L engine to the next level of performance with high-flow CNC cylinder heads and revised intake to deliver 444 hp and 380 lb-ft–plus of torque on premium gas.) Second, this car is being built for serious driving; even occasional autocross use, so the engine has been moved back, bringing the front spark plug slightly behind the front axle centerline. This helps balance the weight between the front and rear of the car.

As with any metal fabrication process, it’s always a good idea to plan ahead, and make at least a mental checklist of all of the steps for the process. First, Ladd’s crew took careful measurements from the new engine and transmission, and these dimensions were used to determine the size, shape, and location of the new firewall recess, and to plot exactly where the Drake Hot Rod firewall would be cut away.

With the plan worked out, they carefully laid out the cut lines on the center of the firewall, double-checked everything, and then used an abrasive wheel in a hand-held grinder to cut the opening. With this step completed, careful dimensions were taken for the new firewall recess, and these dimensions were transferred onto a piece of 18-gauge cold-rolled steel sheet.

Ladd has made a special radius-bending attachment for his manual leaf brake, and that allows him to make beautiful, rounded corners for items like this firewall recess. Four carefully laid-out bends were required for the recess, and the blank was made slightly oversize to allow for trimming later.

Once the recess could be fitted into place, several areas on the old firewall required a “tune-up” to allow a precise fit. With these modifications made, the new insert could be properly positioned, and the upper edges and the sides were marked for trimming.

The abrasive cut-off wheel was used again to trim the upper edge of the new recess, and the cut edge was trued and smoothed with a small handheld disc sander. The sides of the insert were rough-cut with the cut-off wheel, and since these edges were completely straight and flat, they were hand-trimmed with aircraft shears.

Once the edges of the recess were finished, a filler piece was made to attach to the top edge. This was carefully laid out, then rough-cut with a bandsaw, and tuned-up with a hand sander. When this was completed, the top edge of the insert was rounded-over with a special set of “tank” dies on a power beading machine. This edge was curled to about 45 degrees, with the idea of curling the edge of the metal it would mate to as well. This strategy creates a beautiful rounded edge, and even more importantly, the strength provided by the curl will go a long way toward keeping the metal from distorting from the welds.

Next, the top edge of the recess was curled with the beading machine, to match the top filler piece. Then, the recess and the cap strip were tack-welded together, the joint was worked with an Eastwood hammer and dolly to smooth out any irregularities, and the panels were finish-welded together with a Miller Diversion 180 TIG welder.

The next step was fitting the recess assembly into place to check the fit one last time. After the final adjustments were made, the new recess was tack-welded into place, and all the joints were worked with a hammer and dolly. There were two small areas at the edges of the recess that required special care because of the extreme convolutions required there. The solution was to cut a small section of metal away and fashion properly contoured filler pieces. These were carefully fitted into place, tack-welded, and trued with a hammer and dolly in preparation for the finish welding.

After giving everything one last inspection, all of the panels were welded together. If you look closely at the photos, you’ll see the strategy the Hollywood Hot Rods crew used for this sensitive job. They made a series of small welds, about 1-inch long, skipping 6 or 8 inches away for the next welds. This “skipping around” technique is great for keeping the metal as cool as possible, which keeps distortion from welding to a minimum.

The final steps were sanding the convex tops off of the weld beads, raising any low spots with careful hammer and dolly work, and re-sanding until everything was perfectly smooth. As you’ll see in the accompanying photos, the end result is superb; the new firewall recess is just as straight, smooth, and uniform as a die-stamped part, and it is entirely consistent with all the other top-quality work being done on this project from start to finish.

Keep an eye out for the next stage of the Road Tour ’40 project. We don’t want to give it all away, but have you ever wondered if the classic shape of the ’40 Ford roofline could be “sweetened”? You’ll love seeing the next steps being planned by the talented crew at Hollywood Hot Rods.

Tools You Will Need

5-inch right-angle electric grinder, Abrasive cutoff wheels, 2- and 3-inch right-angle pneumatic sander, 2- and 3-inch sanding discs, Aviation shears, Body hammers, Dolly blocks, Pneumatic die grinder, Thin 3-inch cutoff discs, Magnet, Tape measure, Scriber, Straightedge Circle template, Marking pen, Bandsaw, Tank dies for bead roller, Power deep-throat bead roller, Miller TIG welder, Sheetmetal bending brake

AMSOIL Inc.
(800) 956-5695
www.amsoil.com

Dennis Carpenter Ford Restoration Parts
(704) 786-8139

http://www.dennis-carpenter.com/

Hollywood Hot Rods
(818) 842-6900
www.hollywoodhotrods.com

The Eastwood Company
(800) 343-9353
www.eastwood.com

Miller Electric Mfg. Co.
(920) 734-9821
www.millerwelds.com