And now for something completely different.....

[Woznaldo]

I think the GTT handles pretty well out of the box but, like most things, it can be improved upon.

Rear diffusers are becoming more popular within club level motorsport and can be made for relatively little cash (under 100 quid) but would it be worth the effort on a GTT track car?

I understand that to make the most of a diffuser, the rest of the underside of the car must be as clean and flat as possible and that it is not going to be worth the effort unless this is done.

To evaluate whether or not it's going to help we must first look at our starting point. That being a lightweight FWD hatch. It has a tendency to understeer, which can crudely be translated to the rear having more grip than the front? A rear diffuser may only add to this problem.

Let's assume that our theoretical GTT has good track proven coilover suspension set up and that the tryes are as good as we're gonna get.

What are your thoughts?

[Mart]

Wasn't there a gtt bodykit knocking around that had a rear diffuser moulded into the bumper? If I remember rightly it looked utter sh1te, and probably about as effective on track as what it looked cool.

A good improvement is to panel off the 'cavity' area where the o.e spare wheel would sit; ie, make it flat between the lower part of the rear beam to the front edge of the lower part of the rear bumper.

[rs250nut]

I would want to look at the weight balance first

[Woznaldo]

I'm not talking about a styling exercise. I'm thinking of genuine attempt to improve handling/grip/balance. That's why the underside of whole would need looking at.

Yes we can look at balance but what can we do to improve that? Relocate battery? Ultimately it's a FWD car the engine & gearbox sitting if front of the front axle. We can try to improve weight side to side.

Would there be better gains by investing time into a wider track? Williams kit or custom set up?

[J$£5GTT]

i think its a lot of effort for not a lot of gain really,
the 5 was born with aerodynamics of a brick an
i dont thinka rear diffuser is gonna make the
slightest bit of differance

[5alldaway]

how about sticking on one of them rear diffusers from the 197, or some of those hedgehog spikes like on them new evos?

[Chris Hebden]

As far as i understand a diffuser pulls the back end down, therefore on a FWD car this is going to be scary around fast sweeping bends! As Mart said i think there would be gains to be made if you made the underneath more "streamline"

[Woznaldo]

OK, like i've already mentioned, the diffuser is not worth doing unless the rest of the underside is smoothed too.

A proper front splitter with extended lip as part of a flat tray attached to the underside of the front subframe. After taking some rough measurements, the tray would need to be about 20-25mm below the lowest point on the subframe to ensure that it will clear the lowest parts of the engine/gearbox (gear selector shaft, eng/gbox support brace), this would still leave the exhaust front section sitting a little lower still (my car has 2.5" system).

The front splitter and tray would help exert positive downforce on the front of the car and could also help force airflow through a FMIC and Radiator (with some ducting), although it would be equally important to have somewhere for the engine bay airflow to go to.

If volvo bothered to fit aerodynamic aids to their 240 when it was competing in Touring Cars then there might be hope for the upsidedown skip.

[rs250nut]

I looking in to the willy wide track at the moment as I have a williams in the garage that im breaking.The rear beam is also wider so im told.

[Woznaldo]

I remember from the old site that the Williams wishbones bolt straight up and are the same part as R19 16v wishbones. The rear beam is exactly the same as the std Clio 16v which is wider than the GTT beam.

I think the problem that didn't get cleared up was if the Williams or R19 16v driveshafts could be used?

[rs250nut]

I thought that you would have to use the willy subframe as well, diffrent dampers would be needed as well unless you changed the position of the shock mount with some adj top mounts.

[Woznaldo]

Wishbones bolt straight up to the GTT subframe which would leave you with some extra negative camber but I think you could cancel it out with a slotted hole at the strut mount to hub.

Does the willy subframe bolt up to the GTT? I wouldn't have thought so but, have no idea?

[Woznaldo]

I will continue to research some more on the aerodynamic aids, specifically a clean body underside. I've found quite a bit of useful stuff on the net including an article in Racecar Engineering.

I think there could be some gains to be had for a track car. I might just have a crack at making up a template with some plywood/MDF.

Don't expect any results anytime soon as i'm still trying to get my car registered in Oz so, i'll up date the post some time in early 2020!!!!

[Matt@CodeRedMotorsports]

The Williams subframe shares the same dimentions as GTT subframe, the only difference is the williams has a triple skinned lower section, the R19 16v and williams lower arms are the same dimentions but different part no's......to use a 'wide track' from williams you will need a williams anti roll bar and the driveshafts and struts, there was talk of using the R19 16v anti roll bar and the drivers driveshaft, but you still need the passengers driveshaft from the williams.....
As for the front splitter, 40mm from the road surface and 15/20mm in front of the periphery of the car worked best for me.........Marine ply extending back to the last part of the subframe, plus a slight 'angle of attack' toward the front of the car i.e. front slightly lower than the rear.
I set my car up so the rear traction is slightly......destroyed? to be able to get the car to turn in under braking.....(left foot braking).....
As for the rear end of a clio 16v.........hardly worth the effort.........you would get the same effect with spacers...you could always load up the rear torsion bars, via the anti roll bars, by rotating the the centre block, but trickey to get right and fiddly to line up the torsion bars afterwards, if you do this mod, remember to cut a retainer into the anti roll bars to stop them from shifting.....a split pin at each end does the trick......

[Matt@CodeRedMotorsports]

Sydney is a great place by the way!
I stayed in Kings Cross area when I did my world trip......

[Woznaldo]

Thanks Matt, I must admit to enjoying Sydney quite a lot! Been living here for 2 years now.

Matt have you actually fitted the driveshafts for this conversion? Does the Willy roll bar fit the GTT subframe when using the Willy wishbones?

Were you using the splitter on a GTT or Clio? The lowest part of the car (apart from the wheels) has to be not less than 100mm in Oz for street regulations. I not read whether or not that will still mean that a splitter will be effective?

[Matt@CodeRedMotorsports]

PM mate...