Aero splitter

Making the splitter

To use the profile, you will need to assemble the printed A4 sheets. The order should be fairly obvious - 11 to 17 across the top, and 21 to 27 below. The guide line at the side of one should be 63.5mm (2.5 inches) from the line on the next sheet. This will correct for any offset that might occur during printing. Cut round the outline and use it to mark out the sheet of ply. Also mark the hole positions and glue a pair of spacers cut from the 5mm ply at positions A2 & B2.
Alternatively, create your own profile - see photos. Once you have cut the profile, it can be sanded to prepare it for painting.

Also I have profiled the leading edge in the hopes of improving the airflow by creating an elliptical radius on the lower edge

The profile for the rib supports is on the second page. I used four, equally spaced from one end of the squared off cutout in the main piece to the other. The two inner ones will need to be trimmed to allow for the bracing bar. You will need to work out the dimensions to suit the piece of wood you will be using.
I attached them with 3 4x25mm screws, adding the glue for the final assembly.
The venturi panel measures 800x250mm, and was screwed along its leading edge at 100mm intervals. Along the ribs the spacing for the first five from the leading edge were spaced 20mm apart, and the next five at 30mm. This was sufficient to pull the panel down onto the curve of the ribs. It also has to be screwed to the bracing bar at the back - I used the same spacing as at the leading edge - otherwise you are left with bulges between the ribs which look a bit odd!
I painted the inner surfaces before finally gluing the panel in place. Make sure the screw holes are sufficiently countersunk so that the screwheads are slightly recessed. Then once finally screwed & glued, fill the screwholes and smooth off prior to painting. Use a thick-bodied wood primer so that it can be well smoothed off prior to applying the top coats. A grey primer from Halfords will allow some more wet & dry work if you’re fussy, with a final top coat of gloss paint in a colour of your choice.

Mounting the splitter
You will need two pieces of wood 20mm thick, 85mm long, 40mm high for the central supports, with the front shaped into an elliptical profile - for appearance only, as there is no airflow past them! Drill two holes in each to correspond with the holes in the splitter to take 5x75mm screws.
When I had attached the splitter to the front bumper, I felt that there was too much flex, and in the hopes that it was going to generate some downforce, I decided to add some further support to the trailing edge. I found that the bracket that is bolted to the front of the subframe and carries the plastic baffle was well placed to provide an anchor. Fortunately for me, it appears that a new part was fitted when I had the TF subframes installed, as there were no corroded bolts to undo. I had to slightly rebend it to make it line up correctly with the splitter. I fixed a length of aluminium angle to it in place of the baffle. With some wood blocks bonded in place, a panel of 5mm ply could be attached with woodscrews to it, and to the bracing bar of the splitter assembly. I had to add some 5mm spacers to get it to sit straight on the two faces. See the photos for details.

Materials required -
5mm marine ply - a 2,4 x 1,2m sheet will cost about £40, but will make two complete assemblies. For one, the sheet needs to be cut lengthwise to 2,4 x 0,6m.
12-15mm wood for the ribs; 20mm wood for the two supports.
Some approx 25mm square section for the bracing bar.
30x20mm aluminium angle (from B&Q)
Woodscrews to pull the venturi panel into shape - 6x3/4 for the leading edge, 6x1 further back (or the equivalent 4mm screws). 4 off 5x75mm screws for the central mounts, and 4 off 4x25mm for the outer attachments. I used Turbogold screws from Screwfix.
Glue - I used Evostik Polyurethane Wood Adhesive (catalogue no 40778 at Screwfix)
Paint - I used a stain-blocking wood primer that I happened to have, applied generously by brush. It got a fairly thorough rub down on the areas that will be visible. After that I just used Halfords panel spray aerosol grey primer and gloss black. The final quality of the finish is up to you!

As with the proprietary splitters, it is intended to control the airflow a bit better, reducing front end lift. I have tried to go a little bit further by adding a curved surface to the underside. This hopefully creates a venturi effect, accelerating the airflow under the nose. If successful, this will slightly lower the air pressure, adding to the downforce. I have made a pair of endplates to try to achieve the best efficiency of the venturi, but it remains to be seen if they survive any encounters with speed bumps, ferry ramps &c! The venturi bottom edge is in line with the bottom of the front antiroll bar (TF type because of the suspension mods), so I hope it will not be at risk. The endplates are removable, so I could even fit a deeper pair for track use ;-)