There may come a time when your factory gas tank is no longer functional for whatever reason and you look for alternative fuel storage. Maybe your tank is too small and you seek additional fuel capacity, or your tank has been somehow damaged, or you're simply converting to a fuel cell for safety reasons.
Fuel cells come in three basic varieties: a hard plastic cell, an aluminum cell, or a bladder-type cell. The bladder cell is essentially a large rubber bag fitted inside a steel box. The bladder is designed to absorb the movement of the fuel sloshing with the vehicle in motion. Bladder-type cells are most often used on race vehicles where they can effectively absorb the energy of impact or violent movements.
Our experience has shown that any of these types can be made to work on a noncompetition rig with a few precautions to note. Mounting should take into account the movement and chassis flexing that is inherent in an off-road vehicle. We have seen some of the thinner, basic aluminum fuel cells crack and begin leaking. Long-term flex in this application can fatigue the corners and edges until they weaken and crack.
Fuel cells can be purchased with or without foam inside. Foam baffles fuel sloshing and can prevent an explosion due to violent movement. The foam can absorb the energy of an explosion and help starve a fuel fire of oxygen. Despite its vital function, the foam inside a cell usually occupies only about 2 to 3 percent of the total volume.
In general, fuel cells are not DOT-approved and may not be legal for use on the street. Additionally, a fuel cell will usually not pass a visual test at a smog station. Check your local laws to find out the details for your area.
Plumbing The CellOnce you've got the fuel cell mounted in your vehicle, you'll need to address plumbing it to your carburetor or fuel-injection system. The most common way to do this is to run an external in-line electrical fuel pump, although some fuel cell companies sell complete pump assemblies that can fit inside the cell. Depending on the fuel cell, there are also variations in the filler opening, and various necks and extensions are available to accommodate location of the fill point on the vehicle.
The fuel pickup location can be critical for an off-road vehicle that sees a lot of extreme changes in vehicle attitude. In general, a cell with a dropped sump in the rear works well, or you may consider a cell that uses multiple pickup points inside the cell.
Some fuel cells can also accept a fuel-sending unit if you desire to keep an eye on fuel consumption. We have also seen cases where some owners have managed to adapt an OEM tank sending unit to the flange on the top of an aftermarket fuel cell using a little thought and effort.
Additionally, a rollover check valve should be used with any fuel cell. This prevents gas from escaping the cell in the event you go tires up out on the trail.
Many race vehicles use steel container fuel cells. These typically consist of a flexible fuel bladder encased in a powdercoated sheetmetal enclosure. If you'll be using your rig in competition, always check with your sanctioning body to determine its specific cell choice and mounting requirements. | 
Plastic fuel cells are available in capacities from about 4 gallons up to over 30 gallons, with many sizes in between. Manufactured from polyethylene, these cells come with circle-track corner fuel pickups or rear-sump drag-race pickups, the latter being best for general 4x4 usage. | 
Fuel cells can be purchased with or without foam. The foam uses very little of the overall cell volume but serves to prevent fuel sloshing. In the event of impact or fire, the foam can help prevent explosion and inhibit the spread of a gasoline fire. |