This page is dedicated to the fuel cell we built for the owner of an E39 M5 BMW.

Here is a picture of the standard trunk in the E39. The battery sits under the cover at the bottom and the rounded area at the top is for the flat tire repair kit etc. as the car did not come with a spare tire. This area is known as the "cubby"

The owner purchased a new floor section for the E39 trunk area and shipped it to us to determine what size tank would fit and what was possible with the space.

A closer view of the cubby area. The space extends back under the horizontal bar next to the battery area. This will be put to good use in making the equipment fit.

The first mock-up of a fuel cell and a pump. It will be a tight fit but the 3 gallon cell and ancillary hardware will work. The original plan is to mount everything with a simple aluminum structure to the existing mounting holes around the edge of the cubby.

A look inside at the baffles that are used in the fuel cells we build. The cell is divided into 6 compartments with tight fitting plastic. The plastic is relieved on the left side to allow the splash guard to push down for filling the tank.

Bottom view of the fuel cell top plate. Custom roll over valve and in tank filter/pickup assembly with splash shield under the filler neck.

You can also see the bolts that were welded to the bottom of the plate to act as mounting studs for the pump assembly. This way when lowering the pump down the access hole is simply sets on the studs, there is no fighting bolts into hidden tapped holes.

Top view of the fuel cell plate. The lines to the pump and the vent are installed.

Front view of unit with everything installed.The pump relay also mounts on a stud on the pump plate. The stand-offs were milled down to the ideal height to get the assembly to fit in the cubby with a hard top.

Side view of the assembled unit. You can partially see the rubber bumpers installed at the bottom of the pump bracket to hold the unit in proper orientation even without it bolted tightly to the studs.

Close up of the top of the pump unit. You can see the relay mount. A rubber bumper was installed under the back of the relay to keep it from flexing on its plastic tab and snapping off.

As the project progressed, it was decided a proper cover was needed over the assembly to make it a closed cavity. The decision was made to change from a structure of milled aluminum bars and sheet to a carbon fiber plate as the mounting structure. The sandwich carbon plate is 1/4" thick and very strong, especially considering its weight. The piece was milled to specification and test fit.

Here is the pump access hole with the unit assembled. It is not difficult to get to the lines on either side of the pump or the relay and pump mounting studs.

Here is a picture of the semi-assembled unit. The original plan was to exit all of the lines and electric out the side of the cubby. Due to the close proximity of the aftermarket exhaust to the side walls of the cubby, the decision was made to bring the plumbing out the top and side of the enclosure. Two blue bulkheads(later changed to black) can be seen on the left of the carbon and the electrical exiting out the left side of the battery compartment.

A close up of the electrical. A bulkhead connector for the RJ-45 pump harness was installed and a new color coded wire built for the run to the controller in the car. The pump power wires are run through a grommet to be landed on the battery.

A preliminary look at assembled unit. There was a few pieces of milled aluminum used on the piece.

The completed unit. The black bulkhead fittings for the vent and pressure line are installed. The milled aluminum pieces finished and installed and the wiring completed. The unit was leak and pressure test with the pump run in before shipping. The owner can drop it in the car make the various connections and it's ready to use.

Below you will find various pictures of the finished unit. The aluminum and carbon change appearance in different lighting and can be quite striking. The pump cover plate has the M logo relief milled into the face of the cover and polished. The face is grained to provide a contrast.