Without a doubt, the biggest expense in building a racecar from a production car is having the roll cage installed. That step in the process involves prepping the interior, removing the dash and gutting the doors to accommodate the “Petty bars” or the pyramid X designs.
Some steps are best left to the fabricator, but gutting the doors is a process you can do in your garage at home, which saves you money. It also lets your fabricator focus on the important task of building the cage.
The tools you will need, if you don’t already have them, likely won’t cost as much as the labor the fabricator would charge. You need an angle grinder, and several cutting wheels. It’s probably $50 worth of stuff at Harbor Freight. You probably already have most of the rest of the tools you need: Sharpie, straight edge, ball peen hammer, decent file and a shop vacuum.
You’re going to need to buy the “value pack” of cutting wheels. I think I went through seven or eight of them. You’ll also need safety glasses, hearing protection and an N95 mask at minimum. You should be used to wearing those by now, anyway, right?
You’ve got to remove the window and regulator first. I didn’t document that process because, well, I forgot. My bad. But on a Miata, and probably most cars, just remove every nut and bolt you can find and eventually it comes apart. Some of the fasteners that hold the glass to the mechanism might only be accessible when the window is in a specific position within its travel. If you have power windows, keep the battery and the switch connected so you can move things around.
Once you get the regulator and glass out, you can take the Sharpie and the straight edge to draw the lines you’ll be cutting. Yes, a straight edge. You want to build a nice racecar, don’t you? Where the door bends toward the outer panel, you can hold the Sharpie and your thumb and forefinger in such a way that you can “trace” the contours of the door with your middle finger. That photo below didn’t turn out so well, so I hope the description works. Half the reason I wanted to cut the door up is so I could get rid of a lot of the sealer used to hold the plastic film that keeps out road grime. It’s messy and it gets on your clothes almost every time you open the door.
As you cut through the steel, it’s easier to let the rotation of the cutting wheel pull grinder along, like a chainsaw. If the sparks fly into the interior or hit the windshield, cover them with a canvas tarp or something that won’t melt or catch fire. Those hot little sparks can speckle a windshield and make it look like you drove through a sandstorm. They can do similar damage to a vinyl dashboard. These photos walk you through the process.
This video takes you quickly through the process of cutting out the interior door panel to facilitate the installation of a roll cage.
This video shows a time-lapse capture of gutting a door. Because of the rotation of the grinding wheel, sparks were flying toward the dash panel and the windshield, which we covered with a canvas tarp. Those hot little sparks can speckle a windshield and make it look like you drove through a sandstorm. They can do similar damage to a vinyl dashboard. A welder’s jacket is a good idea, too, if you have one.