Can an Amateur Fabricator Build a Custom Firewall? | DIY Automotive Fabrication
This is how we built a firewall for the first time using cardboard, sheet metal, a welder, and a whole lot of trial and error.
This article includes the entire process from beginning to end of our firewall build, along with the lessons we learned at the end!
When we started building the custom firewall and floor structure for our Dodgeball project, we had a pretty simple question:
Could a couple of guys who aren't professional fabricators actually build a custom firewall themselves?
We weren't professional welders. We didn't have a fancy fabrication shop. We didn't have a CNC plasma table, a sheet-metal brake, or years of experience building custom cars.
What we did have was a project, some basic fabrication tools, a welder, some cardboard, and the willingness to figure things out as we went.
And that's exactly what we did.
Over the course of seven episodes on The ROY Garage, we took a pile of cardboard templates and gradually turned them into a custom firewall and floor structure for our Dodge cab-swap project.
Watch the complete 7-part Custom Firewall playlist on YouTube
The finished product isn't perfect—and that's kind of the point.
This series is about showing what automotive fabrication looks like when you're learning as you go.
Here is Our 7 Part Series
Part 1: Starting With Cardboard
Watch Part 1 — Building the First Section of the Firewall
First things first, had to fill in the floor panel which goes around the brake pedal.
We started with some cardboard.
Got the piece dialed in and transposed it to some sheet metal.
Cut it out and tacked it into place so we could test fit it.
We couldn’t quite get it to fit around the foot pedal, but after some cutting and test fitting and some more cutting and test fitting, boom! It fit!
Looks pretty rough but that’s okay, a few min, or an hour with the grinder and it will look perfect!
We could finally say we are making progress! And we can move on to the next step - adding some structure to this firewall.
Part 2: Building the Supporting Structure
Watch Part 2 — Building the Firewall Support
After cutting a big hole into the firewall to make room for our Chevy drivetrain, we knew we would need to add some rigidity to the cab. We decided to run two thicker piece of steel from the corner of the firewall to the bottom of the floor pan. Start with some cardboard, again.
We made a template to the best of our abilities and cut out one side of the steel rod.
Then we test fit the rod as kind of a double check to make sure our template was just right. We used a white marker to mark the next cuts.
Once we felt good, we tacked it into place, thought it looked good enough, and laid the final welds.
What do you think of our welds??
With the driver's side done, we shifted to the passenger side of the cab.
Part 3: Adding Rigidity to the Passenger Side
Watch Part 3 — Mirroring the Firewall Structure
The coolest thing about Cardboard Aided Design is if you need to mirror a piece, you just flip it over!
This piece is for the driver’s side.
And now it is for the passenger's side!
Looks pretty good - right??
Looks like our angle here is off a little, but it’s not too hard to just make a new piece.
Then we marked the top.
Don’t forget to prep your weld areas first by removing any rust or slag!
We cut out the next piece.
Tacked it into place.
And then finished welding it when we knew it was just right!
Next, we bolted the floor plate to make sure everything was still fitting correctly.
We kind of boogerd this one up, but nothing a grinder can’t fix!
Part 4: Designing Around the Pedal and Engine
Watch Part 4 — Firewall Support and Pedal Placement
Time to add a piece that connects the driver's side and passenger's side. We also figured this would be a great place to mount our gas pedal.
Using some more cardboard.
Double-checking fitment and how our firewall is lining up with the engine.
Once we were happy, we cut the piece out of angle iron and used some duct tape while we made the joining piece.
Then transposed and cut!
Don’t forget to prep the weld areas.
Tack into place.
Now we are double-checking fitment before pulling the piece out and finishing welding it together.
Since we are not professional welders, we had to spend some time grinding down our welds to make this look a lot better.
Now we laid our final welds.
Then we eyeballed where we wanted to drill the first hole for the gas pedal.
Marked the second hole, drilled it, and installed the pedal.
Looks pretty good, right?
With the rough skeleton laid out, it is time to start filling this firewall in!
Part 5: Turning Cardboard Into Steel
Watch Part 5 — Cutting, Bending and Welding the Firewall Panel
This episode really shows the basic process we used throughout the build.
Cardboard → steel → cut → bend → test fit → adjust → weld.
First, we need to cut a small piece out from this huge 4x8-foot piece of steel.
Make sure you have all your PPE on!
You should have some good tracing skills by now!
Cut it out!
Next, we needed to do some bending. With the piece, we were able to put it in the table vice and use our bare hands to bend it.
After a few attempts of bending, checking fitment, and bending some more, we had it!
We then used the magnet that came with our Lincoln Electric welding kit to hold it in place while we tacked it
Then we laid the final welds after adjusting the welder a little bit lol.
We then did the other side.
After doing these two small pieces, we were ready to make a big one that would really start to fill in this firewall.
Part 6: Getting the Main Firewall Section Fitted
Watch Part 6 — Fitting and Welding the Main Firewall Section
By Part 6, the firewall was starting to look like an actual structure instead of a collection of random pieces.
We took another cardboard template and transferred it to steel.
And cut it out.
This time, we cut along the line that we wanted to bend so it would be easier to bend. You can see it a lot better in our YouTube video.
Easy peasy!
We used our bench to add some bends to the side pieces.
Then we added some small tacs to hold it in place while we filled in the slivers leftover from our far from perfect template.
Then we used some spare steel to fill in the slivers.
We were not patient enough and experienced some pretty good warpage.
So we had to get creative…
After we got it just right, we moved on to the inside of the first bend we did. Since we removed some metal, it did need some reinforcing.
Then we held the piece in place and marked some more cuts we needed to make.
Seen here on the bottom of the piece in the image below.
Then we needed a little more bending done.
Next, we moved on to cleaning up the sides of this firewall piece.
We had a bit of a gap and decided the best course of action was to cut a sliver out of the top of this piece, bend it into position, and weld it back together.
It worked perfectly! So then we cleaned up our welds - which took a while…
Lastly, we tacked it into place! It is starting to look like a firewall!
Lee, admiring the hard work.
Part 7: Finishing the Firewall
Watch Part 7 — Finishing the Custom Firewall Build
The final push! We turned one hole into two… But the are at least smaller now and don’t require any bends!
This is the passenger side template and…
This is the driver's side template. You know the drill!
Trace and cut.
Test fit!
Tack into place!
Look at that!
We did it!!
After some clean up and paint, this will look amazing!
What We Learned Building a Custom Firewall as Beginners
After seven episodes, these are the lessons we'd take with us into the next fabrication project.
1. Start with cardboard
Seriously.
Cardboard is cheap, easy to cut, and easy to modify.
Before cutting expensive sheet metal, make a cardboard version.
2. Don't try to build the entire thing at once
Break a complicated fabrication project into small sections.
Instead of:
“I need to build a firewall.”
Think:
“I need to build this one piece.”
Once that piece is finished, move to the next.
3. Test-fit everything
Then test-fit it again.
And again.
The more complicated the shape, the more important this becomes.
4. Leave yourself some extra material
If you're cutting sheet metal, don't immediately try to make the final cut perfect.
Leave yourself some room to trim.
It's much easier to remove metal than add it.
5. Clean metal matters
Before welding, remove paint, rust, corrosion, and other contamination from the welding area.
We found that preparation made a huge difference in how easy it was to weld.
6. Tack weld before fully welding
Tacking gave us a chance to see what the piece actually looked like in the vehicle before committing to a bunch of welds.
That saved us more than once.
7. Welding can move your metal
Heat changes things.
A piece that fits perfectly before welding might move once you've put heat into it.
Don't be surprised when you need to make adjustments.
8. Think about serviceability
Ask yourself:
“How am I going to work on this five years from now?”
Make sure you can still access important components, bolts and hardware.
9. You don't need a perfect weld to keep learning
We're beginners.
Some of our welds looked good.
Some needed grinding.
Some were definitely better than others.
But every weld taught us something.
The goal wasn't to pretend we were professionals.
The goal was to get better.
Is Building a Custom Firewall as a Beginner Possible?
Yes—but don't confuse “possible” with “easy.”
We wouldn't recommend looking at a complicated automotive fabrication project and assuming you'll get everything right the first time.
You won't.
We didn't.
You're going to make mistakes.
You're going to cut something wrong.
You're going to discover that your cardboard template wasn't quite right.
You're going to weld something and realize it pulled the metal somewhere you didn't want it.
You're probably going to grind some welds back down.
And that's okay.
That's fabrication.
The important thing is learning how to solve the problems when they show up.
Want to Start Your Own Project?
One of the reasons we created The ROY Garage Project Planner is because projects like this can get overwhelming really quickly.
There are always 50 things that need to be done, and it's easy to look at the entire project and feel like you're never going to finish it.
Breaking the project into smaller jobs makes it much easier to make progress.
One piece. One task. One weld. One day at a time.
That's how we're building Dodgeball.
And that's how we're building the life we want.
A Note for Other First-Time Fabricators
Everything shown in this series is based on our own learning experience.
We're not professional automotive engineers or certified fabricators, and this article isn't intended to be a substitute for professional engineering, welding, or vehicle-safety advice.
If you're building a structural component, firewall, floor, roll-cage structure, or anything else that could affect vehicle safety, make sure your design and materials are appropriate for your particular vehicle and intended use.
Learn, measure, test, and when you're dealing with something safety-critical, get qualified help.