Hey Guys. I started tearing down a 29/29 A Cowl this week with the intention of selling off the lower firewall with enough parts for someone to peice together a Roadster Pickup Body. On closer examination I decided that doing so would be counter productive, as I would need to source another one in the future as the long term goal is to piece together a full rolling coupe or roadster to sell off. I figured that if I was shaping up new cowl sides, doors, cab panels, dash and hood that it would make sense to do the firewall as well, so I started googling images getting ideas for the layout and design. Once I was happy with that I made up a model out of cerial box cardboard.
Once I was happy with that, I got to work roughing up a 1:1 out of heavy duty cardboard and masking tape. After deciding on a five inch recess, I used an old plastic hubcap to trace around the base for the transmission flange and cut it out. This is how it looks at the moment.
The main issue is in regards to the transmission housing it’s self. Not having a dummy engine block and transmission I can use as a mock-up, I made the transmission opening slightly larger to accomodate big blocks. It measures 16.5 inches wide by 8 1/4 inches high. These measurement are taken from the base of the firewall.
So the question is whether this opening is big enough to accomodate a big block Hemi, Ford or GM engine with an automatic transmission based on the five inch recess ? This is really important because I want to piece this all together in the next week so I can sell it. So if anyone has a 28/29 Model A with a firewall of similar design, that I can source measurement from, I would be very grateful.
If the plan is just to sell it, I would only make the firewall top, and nothing else. As a long time driver of Model As (41-years), I would not ever recess a firewall 5". I would remove the bottom of the '28-'29 firewall, as it kicks forward, and make a flat replacement. Then I would stretch the frame to accommodate the larger engine. On this one, I eliminated the flange, and made it flat: On this one, I did not (customer request):
That’s something to consider, it’s certainly less effort and uses less steel but I am not sure if the buyer would be running a longer frame or not. Whether or not I recess the firewall, I still need measurements for the transmission tunnel, because if I do end up making a flat firewall, the radius may need to be larger. Out of curiosity what gauge steel did you use for your firewalls ? I was thinking of using 16 gauge, but I am wondering if I should use 14 guage.
If I was to buy it I would rather make my own firewall to fit engine and engine placement. On my '30, I did not cut the firewall at all, just made the frame a little longer to fit the motor. I would think 18 or 19 gauge would be more in line with what the firewall was made of.
I am starting to think along the lines of what gimpyshotrods was saying about a flat firewall. At the end of the day, all it really needs to do is hold the two sides together so that the gas tank can bolt over the top.
Yeah, there’s way to many variables to accurately make the lower with out having the exact car/chassis on hand. Make a flat one so it holds it all together and gives the new owner a starting point and call it good.
Have you considered a wheelbarrow? Kids like us used them for years. The trim up easy, and they have character. This is the only picture I have, but you can imagine...
I don't recommend the wheelbarrow for a Model A. I put a wheelbarrow for my firewall recess in my 49 Ford PU and widened it 8" to fit a 390 Ford under it. It takes up a lot of space under the dash inside the cab. I put a 2 1/2" recess firewall in my Model A to fit a SBC. It doesn't take up much interior room at all. I just had the local sheet metal shop cut it out and bend it to shape, then I welded up the seams.
I never use anything thicker than 18ga. If you are not installing an engine and transmission, don't install accommodations for them. That takes AWAY from value.
I think the wheelbarrow is 16 ga. I used 14 ga for the firewall on the Model A. On the tranny tunnel on my '49, I used 14 ga, and I used 16 ga for the floorboards. I also used the same gauge thickness on the firewall and floor panels on the '35 Ford PU which I sold. On my '34 Ford Sedan, its firewall recess is 16 ga, and I think the repo floor panels are 18 ga (they might be 20 ga, whatever the aftermarket replacement panels are, that's what they are) but they have all the stock contours stamped into them to make them more rigid. On the panels I make, I used the bead roller and it takes a couple of passes for the thicker metal, but I'm happy with how they came out.
Thanks for all the feedback guys, after careful consideration, I have indeed decicided not to worry about recessing the firewall or adding a transmission tunnel. As a number of you have rightly pointed out, it’s a lot more effort. Its also pointless trying to second guess what engine transmission combo the buyer will run. The firewall will basically the same as the original without the humps.
The Jalopy Journal
