Our Fastruck project got this fuel cell mounting. Two square tubes run across from framera
The fuel cell is a bladder inside a metal can. The bladder may be in the form of a plastic tank or a rubberized, flexible balloon. It can be mounted high in a dirt track car or low in a pavement car. It can be mounted to the right side, the left, or in the center, but the most important thing is it is mounted securely.
A boat tank, G.I. can, or anything similar is not a fuel cell. Some years ago, I saw a boat tank welded to the trunk floor in a Hobby car. I didn't inquire as to the condition of the welder.
Realize that your 16-gallon fuel cell could weigh as much as or more than 1,000 pounds in a crash. That is what must be kept in mind when you design the mountings for your fuel cell. Just to give you an idea of how much weight we're considering here: One thousand pounds is the weight of two complete small-block Chevy engines. This is also the reason a plastic bladder should be in a steel can.
The plastic tank with a couple of straps around it might stay in place where the straps are located; however, the plastic tank can and will deform under load. This deformation will reach a stress point where the tank is held, possibly causing a rupture. If an object such as a piece of bumper or nerf bar were to engage the plastic tank while it is distended, you could have something not unlike an excited water balloon, except at that time you would wish it were filled with water.
So much for the scare stories. A plastic bladder inside a steel fuel cell is the proper way to protect yourself.
On an IMCA Stock Car, the rules didn't allow mounting the cell through or below the trunk
On a dirt car such as an IMCA Stock Car, the fuel cell, by the rules, must not be mounted through the trunk floor. Strapping the cell to the floor is a poor choice. The sheetmetal here may be rusty or otherwise weakened. In my IMCA Stock Car, I built an "X" of tubing in the rear frame area, bracing the frame. Then, I welded two pieces of 0.095x1-inch square tubing to this brace. The square tubing was then level with the trunk floor. The 11/44x2-inch steel straps were welded to the square tubing, and they completely surrounded the 12-gallon ATL fuel cell. The X-member in the frame provides a substantial area for the fuel cell brackets to mount, and without the X-member, the chassis would be weak in the rear.
The area behind the cell should always be protected. In this case, I bent some 0.095x131/44-inch tubing to a 45-degree angle on each end. It reached from framerail to framerail and leaned back at about a 45-degree angle. It was as tall as the fuel cell and inside the trunk. In a rearend crash, even if a car wound up on top of my trunk, the offender wasn't going to reach my fuel cell.
I see a lot of fuel cells mounted on the lip around the cell. This lip is not a mounting flange. It can be used for supplemental mounting and for lateral location, but it cannot be the only mounting. A square tube frame fitting the fuel cell and attached to the chassis is a good start.
Since the trunk floor was rusty, it was deemed not strong enough to hold the fuel cell.
Held in place by this lip on a frame and bolted all the way through, the cell should be strapped all the way around with a minimum of two 31/416x2-inch steel straps. Bent and fitted properly, the straps should be welded to the square tube frame. You should have as good and safe a mount as possible if it is built in this fashion.
There are other ways to mount a fuel cell. One way is to build a square tube frame not unlike a box. This type has square tubing down each side and across the bottom. It can be a strong way to encase the fuel cell, but I like the steel straps better because they can flex in a crash. The square tubing corners can break at the welds, and there could be puncture-making ends.
So far we have looked at the physical restraining of the fuel cell, but there are other things to consider. First is the location: up, down, left, right, or center? The one you choose depends on the type of racing, how long your races are, and even what fuel you use.
Let's start with down. If you run on pavement, you want the lowest possible center of gravity. Therefore, the fuel cell should be low. How low? It should not be the lowest thing on the car, but it can be as low as the framerails. Whatever its height, there should be substantial bracing behind the fuel cell. This bracing must extend to a point at least as low as the cell.
Bending the 31/416x2-inch steel straps is not difficult.
If you are racing on a paved track, the cell should be mounted to the right. This is more important if you run long races in which you burn so much fuel that the crossweight changes. If you use alcohol, you will burn fuel at a much faster rate. This weight change tends to tighten the car as fuel (weight) is burned, and at the end of a race, it is better to have the car tighten up than have it get loose.
On a dirt track car, up is better because you need weight transfer. Mounting the cell high, not extremely high, but let's say on the trunk floor, aids weight transfer. This is a protected spot in the car as well. If you are using gasoline and running 20-25-lap races on a 11/44-mile bullring, the side on which you mount the fuel cell won't really matter. You probably won't use more than a couple of gallons. In this case, the loss of 15 pounds from a 3,200-pound stock car is not going to be noticed. On the other hand, if you were using alcohol, you would lose maybe 30 pounds. That might begin to be noticed, so mount the cell to the right.
For left weight, such as when using a 16-plus-gallon fuel cell filled for ballast, mount the cell to the left. Keep in mind that this corner usually takes a lot of abuse. Extra bracing here adds left and rear weight as well as protection.
No matter how well you have mounted and protected your fuel cell, remember to have a metal firewall between the fuel cell and the driver's compartment. It should have no holes.
Route fuel lines inside framerails or out of the driver's compartment. Any fuel line near the driver should be protected with larger steel tubing or placed outside the cockpit.
Here is an example of how not to mount a fuel cell.
This is another don't. Using a square tube framework to bolt to the flange is only good if
Make sure that there is rear crash protection wherever your fuel cell is mounted.