Yes, the unviversal diffusers would be nice, provided you can make enough room for them by modifying the exhaust and this is not something I'm willing to do. At this point, I'm thinking of a rear wing for rear downforce and a splitter or/and air dam for front downforce. For the front, the most effective until now would be the
VWRacing air dam (they don't run a splitter on their racing cars and I don't know why since that would bring extra downforce). For the rear, the wing I'm looking at for the moment would be the 225mm wing from here >
http://www.reverie.ltd.uk/Downloads/Universal%20Brochure%20Wing%20Comparison.pdf . They also have smaller 110 and 150mm but they seem to small and the 300mm wich is too big. Optically I would choose the 225mm with a 1400mm span (1100mm is the width of the car at the upper trunk lid) so it would stick out about 150mm on each side. These extra 150mm will bring even greater benefit since they sit in clean air. On their link, at 8deg AOA and 100mph, the 1400mm span wing can bring about 600-650N (65Kg). Now, you said the Golf has about 5kg lift at the front and 35kg at the rear so the 65kg added would mean a 65-35 = 30kg of downforce. Is this little or much, I don't know, especially knowing we have to properly balance the car. Probably a too high downforce wing at the rear would lift the front (this can be seen on Reverie's tests on racing cars where they've added 800% more downforce over a street 911 GT3 >
http://www.reverie.ltd.uk/Downloads/ReveriePorscheData.pdf )
Questions with the rear wing :
- For an universal wing we'd probably need custom legs. How will we fix the wing to the upper trunk lid (where the brake light is > this can be seen on Bildon's wing but no close pics to get an exact clue)
- For a 1500kg GTI with 60/40 weight distribution, what would be the best ratio between added front downforce and rear downforce (taking into account the OEM GTI levels of -5kg front and -35kg rear@200kmh)
- What would be the approximate downforce increse with the lowering of the car (most of us already have coilovers with 30-40mm lowering wich should help as well when a front air dam/splitter or rear diffuser is fitted)
- Finally, let's say we bring an addition of 50kg of downforce@160kmh. How much would that increase the cornering g for a car as the one described above ?(let's say with no downforce I get 1.1g at that speed with the mods I already got)