Finding the right derby car gas tank is one of those tasks that feels simple until you're staring at a stripped-out interior with a welder in one hand and a tape measure in the other. If you're new to the demolition derby world, you might wonder why we don't just use the tank the car came with. Well, if you've ever seen a stock tank get pinched between a rear axle and a bumper during a hard hit, you know exactly why we move them. It's not just a matter of performance; it's about not turning your weekend project into a bonfire.
Moving the fuel supply inside the car is the first thing any tech official is going to look for. But it isn't just about throwing a metal box in the backseat and calling it a day. There's a lot of nuance to getting a fuel system that can survive a "bone-stock" heat or a heavy-hitting weld class. Let's break down what makes a solid setup and how to avoid the common mistakes that get people sent back to the pits.
Why the Stock Tank Has to Go
The very first rule of building a car is that the factory tank has to be removed. Manufacturers usually tuck those tanks under the rear seat or behind the axle. In a derby, those are the high-impact zones. As the trunk packs in and the frame rails start to "V" or "up-and-over," that thin sheet metal tank is going to pop like a balloon.
When you install a dedicated derby car gas tank, you're moving the fuel source into the safest part of the car: the cabin. Usually, this means right behind the driver's seat or centered in the middle of the back floorboards. By keeping the gas close to the center of the car, you're protecting it with the cage and the strongest parts of the remaining sheet metal.
Choosing Your Tank Material
When you start shopping around, you'll notice two main contenders: steel and aluminum. Both have their fans, and honestly, both work fine if you mount them correctly.
The Case for Steel
Steel tanks are the old-school favorite. They are incredibly rugged. If a bolt shears off or the mounting bracket bends, a steel derby car gas tank can take a hit without cracking. They're also easier to weld if you're building a custom setup and want to add your own mounting tabs. The downside is weight. Steel is heavy, and every pound counts when you're trying to stay under the limit for a specific class. But for most of us, that extra five or ten pounds is worth the peace of mind.
Aluminum Fuel Cells
Aluminum tanks are the go-to for guys who want a professional look and a lighter setup. They usually come with "bungs" already welded in for your fuel lines and vents. The main thing to watch with aluminum is vibration and flexing. Aluminum is more brittle than steel, so if your mounting system is too rigid and the car's floor starts to twist, you can actually crack the welds on the tank. Most guys avoid this by using rubber bushings or just ensuring the tank is held in a "cradle" rather than being bolted directly through the tank's flange to the floor.
The Importance of the Tank Protector
In a lot of the heavier weld classes, you'll see guys running what we call a "tank protector." This is usually a steel halo or a set of bars that extend from the seat bar back toward the rear of the car, surrounding the derby car gas tank.
The goal here is simple: if the trunk of the car gets pushed all the way into the back seat, the protector stops that sheet metal from crushing the gas tank. It's a literal shield. However, you've got to check your local rulebook. Some promoters are very strict about how wide or how close to the sheet metal these protectors can be. You don't want your protector to be seen as a "frame stiffener," or they'll make you cut it out right there in the tech line.
Lines, Fittings, and Fumes
The tank itself is only half the battle. How you get the gas from the derby car gas tank to the engine is where most fires actually start.
Use the Right Hose
Please, for the love of the sport, don't use that clear vinyl hose from the hardware store. It looks cool for about five minutes until the gas makes it brittle and it snaps. You want high-pressure fuel injection hose. Even if you're running a low-pressure carbureted setup, the fuel injection hose is much tougher and handles the heat and abuse of a derby better.
Routing the Lines
Run your lines through a piece of old garden hose or some plastic conduit where they pass through the floor or the firewall. This prevents the sharp edges of the cut sheet metal from sawing through your fuel line as the car shakes and vibrates. It's a simple trick that has saved many people from a "Did Not Finish" (DNF).
Venting is Key
A derby car gas tank needs to breathe. As the pump pulls fuel out, air has to come in. If you don't have a vent, the pump will eventually create a vacuum and the engine will die. But you can't just leave a hole in the top of the tank. If you roll over, gas will pour out. The best setup is a vent line that loops up higher than the tank and then exits through the floor of the car. This way, if you're shiny-side-down for a minute, the fuel has a harder time escaping.
Fuel Pumps and Safety Switches
If you're running an electric fuel pump, you need a kill switch. This is a non-negotiable safety item. This switch should be within easy reach of the driver, but also accessible to a fire official reaching into the car. If your throttle sticks or a line pops, you need to be able to kill that pump instantly.
I've seen guys mount their fuel pump right next to the derby car gas tank on the floor. That's usually the best spot because electric pumps are better at "pushing" fuel than "pulling" it. Just make sure the pump is protected from debris. A stray piece of gravel or a jagged bit of floorboard can wreck an exposed pump in seconds.
The Pre-Race Inspection
Before you head to the track, do a "shake test." Grab your derby car gas tank and try to rip it out of the car. If it moves even a fraction of an inch, it's not tight enough. During a hit, the forces are ten times stronger than anything you can do by hand. If it's loose now, it'll be a projectile later.
Check your fittings one last time. Look for any dampness around the seals. Even a tiny "weep" of gas can turn into a spray when the pump is running and the car is getting bounced around.
Final Thoughts
Setting up your derby car gas tank isn't the most glamorous part of the build. It's not as fun as painting teeth on the doors or welding a massive bumper onto the front. But it's the heart of the car's life support system. If the gas stops flowing, you're just a stationary target. And if the gas starts flowing where it shouldn't, the night ends in a way nobody wants.
Take the extra hour to double-clamp your hoses, secure your mounting bolts, and make sure that tank is rock solid. When you're in the middle of a chaotic heat and the hits are coming from every direction, you'll be glad you didn't cut corners on your fuel setup. After all, the goal is to be the last car moving, not the one that had to get put out by the fire crew.