The fuel tank is well protected from an impact. However, it’s possible that a crack forms on one of the welds due to a collision or a from vibration fatigue. For this reason, it has always bothered me that the fuel tank is essentially in the cockpit. I considered a fuel cell, but they need to be replaced every five years and there are only two ways to remove one, both of which are onerous in street car with a finished interior:
via the cockpit: If you have a tub, which I do, you need to remove the body, windshield, cage, interior, tub and fuel tank cover panel. That’s a lot of work, but the real issue is that the body requires a massive amount of attention to seal the footbox, side pods and firewall and all of that needs to be torn out and replaced. UGH!
via the engine bay: This requires the engine, oil reservoir, surge tank, coolant swirl tank, firewall, etc. to be pulled which isn’t that bad in a race car which is specifically designed to efficiently pull the engine, but a lot of work for a painted street car. However, the mounting brackets that I welded to the top of the fuel tank would prevent it from sliding through the chassis rails and I would have needed to carefully mount the tank so that I didn’t need access to the interior to reach any bolts. Lastly, I had already installed a permanent fire wall between the tank and engine compartment. So, this approach wasn’t a viable option for me.
Then I had an idea which is always dangerous. I could cut a big hole in the bottom of the stock fuel tank and the monocoque’s floor so that I could install a bladder from the bottom of the car. This would allow me to address several things that I don’t like about the fuel tank:
E85 doesn’t like raw aluminum.
The 2” fill tube doesn’t have a flapper valve. If you roll the car, you’re relying on the flex tube and gas cap to contain the fuel, both of which are attached to the fiberglass body and could be easily torn off. If that were to happen, the opening is 28x larger than the -6 vent that everyone puts a roll over valve on.
The rollover valve should be located inside the fuel tank. Otherwise, it needs to be located in the engine compartment which increases the number of connections, takes up space and creates the potential for a leak if the line between the tank and the valve is damaged in a collision.
Significant modification is required to implement a fuel pickup system (e.g., HydraMat, corner pickups, sump with trap door, etc.).
If you have a tub, you need to tear the car apart (i.e., via one of two options listed above) to service the fuel-level sensor and I’m aware of many builders who have had them fail.
Doesn’t support an internal lift pump without modifications.
No foam to prevent a flame front from forming or reduce sloshing.
The NPT bungs should be ORBs.
The first step was to remove the “finished” low-pressure fuel system and fuel tank. In a previous post, I used dry ice to remove all of the sound deadener from the tank. I then cut the largest hole possible between the 2” x 2” welded to the monocoque’s floor.
Access hole cut into floor. The large size makes it as easy as possible to install the bladder.
After reinstalling the tank, I marked the location of the 2” x 2” chassis tubes on the bottom of the tank. I removed the tank, flipped it upside down on the bench, marked an access hole that left a small flange around the 2” x 2”s and the front and back of the tank, drilled the four corners with a 5/8” hole saw and cut the hole with a 4-1/2” cutoff wheel. There are two baffles in the tank, each with two weld beads on three different edges, which meant that I had to break a total six weld beads per baffle. I accomplished this by cutting the baffle into thirds so that each piece isolated the two beads on each edge. After which I wacked each piece with a hammer to rock it back and forth until the weld beads cracked. The baffle in the picture above was relatively easy to remove because it was in the hole that I had cut. The other baffle was a more difficult to remove because it was tucked inside the tank.
Rough opening cut, baffles still in place
I then clamped a piece of steel to act as a limiter while I ground the edge with a 4” 40-grit sanding disk. As you can see in the picture below, the right side is straight and smooth whereas the top and bottom edges haven’t been finished yet. Because I don’t trust my cutting skills, I left more material than needed which required a LOT of grinding.
Right edge finished, top and bottom edges will be finished next
I then removed the weld bungs for the fuel outlet, fuel return and vent because they protrude inside the tank and would hit the bladder. The easiest way to accomplish that was with a hole saw. Since the existing hole was much larger than the pilot bit, I fabricated drill guides by chucking up NPT plugs in the lathe and center drilling them. I had a similar issue when enlarging the fuel fill hole. In that case, I tack welded a temporary disk to act as a drill guide for the pilot bit (see picture below).
Temporary disk tack welded to act as a guide for the hole saw’s pilot bit
Once that was done, I removed the shift cable tube (I’m using paddle shifters) and the fuel-level sender flange after which I smoothed and deburred every edge in the tank. When I was done the shop was a mess and I had exerted significantly more effort than I had originally anticipated. If I had paid someone to do the work, it would have been much less expensive to have had a custom shell fabricated out of thinner aluminum. I took this approach because I had already mounted the tank and made perfectly aligned cutouts in the in the firewall not to mention that my labor is free.
I drew the tank with the desired fitting locations in CAD and worked with Hill at Agile Automotive to help me spec and order a fuel bladder that solves all of the aforementioned issues with the tank.
All connections are easily accessible via the access panel cut into the floor (the above picture was taken through that opening); fuel outlet (bottom left), motorsport electrical connector for the lift pump and fuel level gauge (middle), and fuel return (top right).
The foam, lift pump and fuel pickup rig is installed/removed through the oval access panel. This enables the fuel bladder to collapsed so that it can be installed/removed through the holes in the monocoque floor and the bottom of fuel tank.
The fuel fill has a flapper value to prevent a leak if the car is rolled. I need to modify my firewall to accomidate the flange and allow the retention clips to be rotated when installing or removing the bladder.
Stock fuel level sender flange has been removed. The new fuel level sender can be easily serviced when the bladder is removed.
The hose end that connects to the roll over valve doesn’t clear the fuel tank cover panel because they weren’t able to locate it directly against the back of the bladder because they needed to provide room for the internal flange. This moves the location forward into the sloped fuel cover panel. I’m on my third iteration of a solution… I’ll figure it out eventually.
The next steps are:
solve the roll over valve clearance issue
clean up the cut out in the floor
fabricate a support shelf for the bottom of the bladder
fabricate a close out panel for the bottom of the car
modify the firewall to accommodate the fuel fill flange
validate that the bladder can be removed and installed using only the two access panels