Building the fastest Lotus Exige in the World

Due to N2s very special 1-off 1-piece roll cage (commissioned by us from Safety Devices as a full FIA spec cage), we were put in the position of having to make our own bulkhead.  Normally, flat sheets of aluminium are used for this job, which work well, but are only really suited to flat bulkheads.  Because we have our harness bar running behind our main hoop (Safety Devices insisted on this to make it FIA compliant), we would have to add a pocket to the aluminium sheet.  We then decided to put our charge-cooler on top of the fuel tank box, which complicated it further by needing a box in the bulkhead going into the cabin.  Finally, after receiving our ATL 70 litre bag tank and seeing how the pump access hatch and fuel filler hatches were arranged on the top of the tank, we realised that our bulkhead was going to land up being a very special shape indeed.

We started off by measuring the cage accurately (it has a 3° rearward lean), and then looking at the size and placement of the charge-cooler plus the inlet and outlet of the tank, transferring it all to CAD and then coming up with a design.

The next stage was to make the wooden buck, which starts as a large sheet of thick MDF (for stability), then has holes routed in it and boxes built up on it, all with 2° draft angles so that it will release from the mould.  Finished off with a 3° bottom flange plate, it was then filled and sanded and painted ready for moulding.

The mould was made, into which the final bulkhead was laminated.  The bulkhead is made from 4 layers of 2×2 carbon twill, and finished with a carbon / Kevlar® final layer to keep the whole thing integral in case anything from the engine bay decides to try to get into the cabin!  The laminte is wet laid up in epoxy, but then vacuum bagged to ensure the laminate goes firmly into all the corners and also has the minimal epoxy in the laminate to save weight.  The result (before trimming down) is a final weight of 1.2kg which is significantly lighter than a fabricated aluminium one would have been.  It also looks a lot nicer too!

We used stiff cardboard to work out the exact shape of the edges of the bulkhead as it goes into the side cill upper sections, then the final shape can be worked out off the car and transferred to the bulkhead sheet.  This will then be cut to shape and then fitted to the car.