improving aerodynamics with OEM parts

[fuscobal]

Yes Bruce , that must be really nice but unfortunately nobody makes such parts for Golf (as they do for Lotus, caterham... in UK). That must be a custom diffuser and I cannot afford paying thousands of euros for wind tunnel testing and custom manufacturing :(

[the bruce]

DIY !!  

The guy who owns the white Golf TDI kit car did it on his own !!


For your bonnet vent plans:

http://autospeed.com/cms/A_2162/article.html?popularArticle

Quite interested in this, especially as I take mine on track.

How hard are the parts to fit generally? Can I do itself by jacking the car up or does it need to be done on proper ramps (i.e get garage to do it)?

For safety and ease of work I prefer a lift.
Fitting all these parts will be possible with just a jack though.

[fuscobal]

DIY is ok if you've got the tech to do it. I've read those articles and while the theory is right those vents, splitters...look awful. I wouldn't put on my car anything that's lower quality than say OSIR ! I care about the look and that's why I'd accept aerodynamic parts from producers that have the technology to do it properly !

Here's an example > http://www.reverie.ltd.uk/automotive_home.php . If someone would make parts like this for our cars it would be awesome !

[the bruce]

What about these?

http://www.reverie.ltd.uk/product_list.php?group=A%20RDIFF&subgroup=A%20RDIFF%20CA

http://www.reverie.ltd.uk/product_detail.php?group=A%20FLOOR&subgroup=A%20FLOOR%20VH&part_code=R01SB0365


My personal preferences are performance, practicability and looks.
After some years spending on modifying cars in this manner I realized
coping all three things in one car is a very expensive task. 

I guess you also know it well.   

[fuscobal]

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)

[the bruce]

Note that 5 kg + 35 kg lift is at 200 km/h. R32 and Golf VI R have similar values.
From what I remember the Scirocco R Cup has a total downforce about 20 - 50 kg
at 200 km/h. I cannot find this data at the moment.

I'm pretty sure adding 65 kg dowforce at 160 km/h will be a significient improvement.
Creating downforce on front for a proper balance will be easier. The VWR + splitter
you told about will be the best way I guess. The VWR looks similar to the Rieger.

The more depth a wing profile has the more efficient it is. You will reach the downforce
to need with less angle. A gurney and end plates increases efficiency even more.

First the suspension has to be setup properly before you add any downforce. There
might be some potential now as you have reduced some weight. But as a last step
with this downforce you will be able to setup the rear suspension more ''tail happy'',
so that handling gets the right way: quick response and less understeer in narrow
corners and ''safe'' in fast corners.

[fuscobal]

Bruce, my car is already tail happy because of the light rear and stiff sway-bar (remember I have 27mm RSB and 26mm FSB). From what I feel from inside the car, it is not understeering at all at this point, but the rear feels a little unstable onhill tops or sudden steering inputs. I made some calculs but won't post them here since we're off topic already. Here's what I found...please add your opinion  > http://www.mk5golfgti.co.uk/forum/index.php/topic,12484.75.html

[malaroo978]

Hi guys, just hoping for some help regarding the plastic spreader rivets. Would a tool like this allow me to install them?

 http://www.halfords.com/webapp/wcs/stores/servlet/ProductMobileDisplay?catalogId=10151&storeId=10001&productId=211934&categoryId=165572&langId=-1

Thanks

[mortygttdi]

Hi guys, just hoping for some help regarding the plastic spreader rivets. Would a tool like this allow me to install them?

 http://www.halfords.com/webapp/wcs/stores/servlet/ProductMobileDisplay?catalogId=10151&storeId=10001&productId=211934&categoryId=165572&langId=-1

Thanks

You don't need a tool to put the rivets in they re plastic and just push in

Darren

[malaroo978]

Thankyou 

[Tfsi_Mike]

 I am going to get the bolt hole in my subframe drilled and tapped and order a new blue motion undertray.

Has anyone considered using a spacer(s) on the 3 bolts to ensure the under tray doesn't contact the subframe?

[the bruce]

Why this, Mike?

[bacillus]

I've got an 06 GTI that unfortunately didn't have the nearside threaded bolt to accommodate the Rear axle cover. Since I had the car in the air, I removed the nut off of the axle cover just used a zip tie to secure that end. It seems very secure so I'm going to leave it that way and not resort to drilling and using a blind rivet stud.

[the bruce]

It seems very secure so I'm going to leave it that way and not resort to drilling and using a blind rivet stud.

I hope it's strong enough, but I'd say drilling + blind rivet stud would be the best option. 

[the bruce]

By far most important:

Drive slow and steady. In a GTI, the highest revs before the turbo kicks in, in the highest gear. Equates to around 56-60mph.

 


From the technical side of view:

- fit OEM aero parts:  http://www.mk5golfgti.co.uk/forum/index.php/topic,22986.0.html
- lowering
- narrow wheels (ET50, 7" wide, no spacers)
- Michelin Energy Savers + increase pressure
- low viscosity oil (0W-30)


At higher speeds air drag is most sigificient. So underbody mods and lowering
will reduce drag by a certain amount:




or buy a Mercedes: