Greetings MUD! I've been lurking in the shadows for a while and it's now time to ask my first real question.
I'm midway through a series of upgrades on my 1971 FJ40, one of which is a 3FE conversion. To support the new motor, I had planned to go the simple route with the stock tank, an external in-line fuel pump, FJ62 FPR and be done with it. After hours spent staring at the truck, at the tank, and the usable space consumed by the tank, paired with the peace of mind of a hard barrier between myself and 18 gallons of fuel, I'm more and more considering going to an underbed tank.
I don't care for the rear ConFerr style tanks, not for any major reason, just a few minor ones: I don't like that it is visible from the rear, distracting from the stock aesthetic, I do not want to modify my fuel fill location, I want to keep fuel weight in front of the rear axle. The more obvious option of using a late model stock tank was considered, but I have not actively searched for one and was looking to squeeze out a little more capacity anyway. That leaves building from scratch. Skills/material to complete this are in hand.
My goal would be a minimum of 20 gallons, 2.7 cubic feet. I spent some time under the truck, and there does appear to be some good usable space in three main regions: 1: A large flat object, thin in height, from transfer output to differential, from frame rail to frame rail. Imagine a big square pancake. Fuel fill would be located in this shape, on passenger side, and (with some pipe work) would route to the stock location. 2: A longer and narrower shape 6" x 8" following the driver's frame rail forward as far as desired and rearward combining with the flat shape in #1, ending at the rear axle. 3: The largest volume would be the area opposite the rear drive shaft, from transfer case extending rearward to the rear axle, likely even passing over the driver's side axle tube on the outboard side, narrow missing a fully-compressed shock. This last area is where an in-tank fuel pump would be placed, more or less as centered in the tank mass as possible.
There are some anticipated downsides: Cruiser lean could be magnified, tight proximity to exhaust, relocation of muffler, difficulty in construction for baffles and general tank build
To 'fuel' the collective mind, here are some photos of 60/80-series tanks that I've pilfered from various threads on MUD, each embrace a little bit of what I'm looking for.
With those concerns on the table, has anyone gone down the path of a custom underbed tank, forward of the rear axle, with larger than stock capacity? Success, failure?
Thank you, Matt
I'm midway through a series of upgrades on my 1971 FJ40, one of which is a 3FE conversion. To support the new motor, I had planned to go the simple route with the stock tank, an external in-line fuel pump, FJ62 FPR and be done with it. After hours spent staring at the truck, at the tank, and the usable space consumed by the tank, paired with the peace of mind of a hard barrier between myself and 18 gallons of fuel, I'm more and more considering going to an underbed tank.
I don't care for the rear ConFerr style tanks, not for any major reason, just a few minor ones: I don't like that it is visible from the rear, distracting from the stock aesthetic, I do not want to modify my fuel fill location, I want to keep fuel weight in front of the rear axle. The more obvious option of using a late model stock tank was considered, but I have not actively searched for one and was looking to squeeze out a little more capacity anyway. That leaves building from scratch. Skills/material to complete this are in hand.
My goal would be a minimum of 20 gallons, 2.7 cubic feet. I spent some time under the truck, and there does appear to be some good usable space in three main regions: 1: A large flat object, thin in height, from transfer output to differential, from frame rail to frame rail. Imagine a big square pancake. Fuel fill would be located in this shape, on passenger side, and (with some pipe work) would route to the stock location. 2: A longer and narrower shape 6" x 8" following the driver's frame rail forward as far as desired and rearward combining with the flat shape in #1, ending at the rear axle. 3: The largest volume would be the area opposite the rear drive shaft, from transfer case extending rearward to the rear axle, likely even passing over the driver's side axle tube on the outboard side, narrow missing a fully-compressed shock. This last area is where an in-tank fuel pump would be placed, more or less as centered in the tank mass as possible.
There are some anticipated downsides: Cruiser lean could be magnified, tight proximity to exhaust, relocation of muffler, difficulty in construction for baffles and general tank build
To 'fuel' the collective mind, here are some photos of 60/80-series tanks that I've pilfered from various threads on MUD, each embrace a little bit of what I'm looking for.
With those concerns on the table, has anyone gone down the path of a custom underbed tank, forward of the rear axle, with larger than stock capacity? Success, failure?
Thank you, Matt
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