Archive for May, 2011

Bulkhead Design & Fitting

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.

FIA Bag Tank

The standard Exige/Elise uses a 40L steel tank that uncomfortably resides within a much larger space behind the cabin.  For N2 to be FIA compliant as well as competitive in endurance races, a much larger capacity of fuel needs to be carried in an approved fuel cell.

Following the removal of the original tank, a new Lotus Sport bag tank to FIA standards was ordered (made by ATL).  The new fully homologated FT3 standard ‘Fuel cell’ neatly fits every available space that the Lotus chassis has to offer.  Construed from a flexible fuel resistant (of course!) ballistic membrane and filled with foam baffling, the cars endurance potential is stretched with an impressive new 70L capacity.  The installation process requires several sharp edges, notches, rivets and holes had to be smoothed and prepared ready to accept the bag tank.

In order to fill this impressive new capacity with fuel, N2 will need to employ a high-flow dry-break system.  The standard holes in the tank bulkhead must be increased in order to accept the large diameter fuelling hoses and associated roll-over valves and breathers.  Working with accurately drawn templates, the tank bulkhead has been cut and all the edges de-burred allowing up to 2.5L a second to be dumped into the cars now mammoth belly.

With the tank closely matching the chassis’ form; it’s no simple task to fit and requires the efforts of a team to squeeze it into its final position, saving just over 4KG on the standard steel tank.

Fuel System Design

One thing for sure is that 400hp is going to need a lot of fuel, so we knew we would have to change the stock in-tank fuel pump. 

On investigation, we found out that the 70 litre ATL Lotus bag tank comes ready to fit the standard Toyota in-tank pump housing.  It can even be used with the standard fuel level sender.  Inside the bag tank there is a compartment for the housing, with special trap doors to allow the fuel to flow into the chamber (on right hand turns) but not back again on left turns.  So we decided to stick with the Toyota system, which comprises a gauze mesh filter, a high pressure injection pump, a secondary finer filter, a collector pot, a pressure relief valve (to return excess fuel straight back into the tank), an outlet to the fuel rail and a breather that breathes both ways unless the fuel level rises or the car inverts.

For the Toyota fuel system to work as we need, we fitted the Walbro 255 litres per hour pump, which is tried and tested and is used by many of the high horsepower Mitsubishi Evos.  This is a longer pump and needs a special aluminium end cap to allow it to fit into the Toyota housing.  The Walbro pump wiring loom is sliced onto the Toyota loom, and this is all that needs to be done. 

 As we are using an open ended fuel rail, we have a return fuel line that needs to be fed into an external adjustable pressure regulator, and then back into the tank.  To do this, we are using the tank pressure sensor required by US Lotuses, and using this as a return port.  As we want to use screwed-on fuel pressure hoses (rather than push-fit plastic pipes as Lotus /Toyota use), we designed our own aluminium fittings that can be fitted to the housing from the outside.  We can now fit proper dash 6 racing fuel hose to the car and not worry about pipes coming off under high pressure!  As the fuel return now comes back into the housing, the internal pressure relief valve is no longer required, so we designed an exact copy of the original valve but machined from solid aluminium which will allow full pressure to be achieved.  The vent pipe continues to work as a vent pipe, and through the MoTec we will be able to use the fuel level gauge (as this is still technically a road-legal car!).

The fuel hose will go directly from the pump housing to the fuel rail, then from the other end of the fuel rail to an adjustable fuel pressure regulator (which will be connected to the induction system so that it takes account of the supercharger boost pressure to raise the fuel pressure), then it goes back to the tank.

Roll Cage Installation

An all new 8-point cage has been designed for N2 with unique detailing and finished to the highest standards.

Bolted into position, the one piece, no compromise cage operates without restriction to either the driver entering the cabin or spotting that important apex.

Unfortunately the cage that you now see fitted to the car was not the original design.  The first version, produced by another manufacturer was scrapped due to the restrictive view out the front screen.  Designed in conjunction with expert cage fabricators Safety Devices, carefully considered routing ensures that the tubes run alongside the A-pillar and roofline precisely, maximising the available cabin space – an important consideration for endurance race driver changes.

The cage connects the front cross beam to the rear steel subframe mounting to the standard roll bar mounts and rear damper pickups along its path.  Featuring a roof brace and a substantial cross brace along the bulkhead and a separate bar for the harnesses to be mated too.  The cage was built to Nitron’s own specification with additional modifications made by Safety Devices to conform with FIA regulations – it truly is a one-off fabrication.  We are really very pleased with the quality of the welding and the thought that has gone into the cage with fine bracing details throughout – hopefully none of which will ever be required!

Clutch and Flywheel Assembly

The lightweight flywheel and clutch plate assembly have been fitted to the engine since recently arriving at NitronUK.

Engine arrives at Nitron!

OK… so maybe it hasn’t only ‘just arrived’ but we have been very busy….

Over the winter months we have been helping our customers prepare for their racing season, developing new products and once again increasing the number of shocks we make year on year supplying to some of the worlds best race teams.

Engine Arrives at Nitron UK HQ!

But now its back to working hard on N2 and we have lots to be progressing with – all very exciting!