MGB GT Auxiliary Fuel Tank

[Ed. Note - I have reservations about placing a fuel tank in the passenger compartment, I would be more comfortable using an approved racing fuel cell consisting of a metal box containing a rubber foam-filled bag such as those sold by ATL or Fuel Safe. In addition, many racing sanctioning bodies require the fuel cell to be separated from the passenger compartment by an additional metal bulkhead. Proceed at your own risk and check your local racing or DOT regulations.]

I am installing an auxiliary fuel tank in my 1967 MGBGT to gain an edge on a long-distance competition that my wife and I enter every year in Georgia, the Damn the Torpedoes Challenge. I thought perhaps others would be interested in this project.

I found that a stock MGB fuel tank (1966-1974) will fit easily in the spare tire well of a GT.

I removed the entire rear spare tire cover and rear seat assembly from the car. I used a spot weld cutter to remove the spare tire hold down from the trunk as it was in the way of the tank and I would be needing it to relocated the spare.

I ground away any surface rust and gave the trunk floor the POR treatment, using Gray as the finish coat. Since the factory tank, which remains in place, is offset to the right it works well to offset the new tank to the left. This gives clearance for the original fuel filler neck and excellent access to the right side of the new tank, which is where the fuel pick up and sending unit are.

MGB GT spare tire well, treated with POR-15. Stock fuel filler neck bottom right.

I set the tank in place and laid some 1" square steel tubing out to mark the length I would need for the left side mounting bracket. I cut the tube to length and welded a mounting tab with a 3/8" hole drilled in it to the front of the tube. I drilled a 3/8" hole vertically at the back of the tube for mounting it to the underside of the rear compartment lip. The tube would have to spaced down at the rear with a bushing to ensure clearance when the spare tire panel is lowered. I was able so space the front by drilling a 3/8" mounting hole in the appropriate location at the front trunk panel.

Measure and cut square steel stock for new tank mounting bracket

Auxiliary fuel tank mounting bracket, welded nut and bolt detail

The right side mounting bracket was a little more involved as the tank has a curve on that side that prevents the use of a straight piece of steel.

I positioned a length of the steel tubing so that the front was a little past where it would need to be and marked it with the actual angle at which it met the front trunk panel. I then marked the tube where the bend needed to be , put it in the vise, heated it up to red hot with a MAP gas torch and bent it by hand at the angle it needed to be to continue it's journey along the tank to the rear of the trunk compartment. Once that was done, I marked where the rear cut should be and cut both ends off.

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At the front I welded another mounting tab with a 3/8" hole and, at the rear, drilled a 3/8" hole vertically through the pipe so it could be mounted to a hole I had drilled in the rear compartment lip. Proper up and down spacing would be handled by the same method as the left-side bracket.

After I bolted the left bracket into place, I laid the tank in position, trial fit the right side bracket and marked where the fuel pick up line was. I then heated the right-side bracket up at that spot and pounded an indentation in it on the underside to make enough space to accomodate the fuel pick up fitting. I then set the right bracket into position. I was then able to position the tank mounting tabs on the brackets and mark where I would need to drill the 3/8" holes that would bolt the tank to the brackets. I pulled the tank back out along with the brackets and drilled all my mounting holes.

Right side aux fuel tank mounting bracket, bent to shape. Note tank offset to left.

Right side aux fuel tank mounting bracket, rear connection detail

I realized that once the tank was in place I would have no access to the left rear mounting bolt's corresponding nut for tightening purposes. To solve this problem, I welded a thick 3/8" washer to the underside of the tube at the mounting hole and welded a 3/8" nut to the washer.

Once this was done, I loosely bolted the left-side bracket to the tank and set the tank in position. I had to leave the bolts loose to facilitate lining the right-side bracket mounting holes up with the holes on that side.

I then loosely bolted the right-side bracket in place being careful to not forget my rear clearance spacer. When it all looked good, I tightened down all the mounting bolts. Luckily I had enough room on the left side to slide a "crows-foot" arrangment from the front of the compartment back to the loose nuts under the mounting bracket. I then tightened them with a wrench from the top. The right side bolts were easy to get to a posed no problem.

The tank was installed and did not even touch the trunk floor. I once again removed the tank and installed some foam padding on the trunk floor where the raised ribs of the floor would be closest to the tank, this in case the tank bottom wanted to flex downward at all when filled.

I cut the new tank's filler neck off so only the verticle portion remained. I took an extra filler neck I had from a car with a non-vented lid and welded it to the verticle neck on the tank. I welded it with a forward angle to it, allowing me to cut as small a hole as possible in the deck to clear the filler neck.

Auxiliary Fuel Tank fitted to MGB GT spare tire well, new filler in deck

I bolted the deck back into position, sans the useless rear seat, and bolted spare tire hold-down to the top of the spare tire deck, installed the spare tire and checked my clearances. I mounted the spare to the rear of the deck and all the way to the left. This left ample room behind the seats for both of our travel bags. Any other things we needed to bring with us on the race could be placed to the right of the spare. Once everything was bolted back in place, I turned my attention to plumbing the new tank into the system.

The new tank will be vented from the existing top vent fitting to the original fuel filler neck on the bottom tank. This will keep any gas fumes from being able to enter the car. I am still deciding on how feed the fuel from the new tank to the existing system, but will keep you posted.