Functional flat underbody and rear diffuser design

[seangti]

Those with coil overs, perhaps also have a look at corner weighting so you know where the weight is sitting. I believe there is a place down at slackscreek with corner weighing ability. They may also be able to offer input as to rebound/spring rates. Some changes could assist balance.

I'm a fan of making incremental changes and measuring. From total stock to adding lowered springs gave me less consistent lap times, but much the same and few more "moments", added the bilstein struts and dropped 2secs a lap on flogged out continental tyres but had great adjustability. Put kumho ku31, lost 1 sec a lap and some on the limit adjustability. This was at QR sprints on their timer, not the gtech. If I did tyres and suspension together I wouldn't know how each affected the other. I also know my max braking g-force and cornering force so can compare forces with speed and time as I make changes to the car and my driving.

It's really just trying to optimise your current set up and ensure you can get everything from it.

Hope this isn't a rant, sorry if it is.

[clicht]

Just get on to a track day and drive, Clint. You've done open wheelers in the past which is far more than most of us here, so don't bother with driver training unless you feel something is "missing" when you get out there.

Yeah, you right...its just the polo is rather different from my race cars, but the basics are the basics....sure I'll see you soon on the track or a good Hill climb

[kaanage]

A road car will be a lot more forgiving and less responsive than an race car so you don't have to worry about being caught out as long as you don't leave the pits and then try to brake and turn in on the first corner like in the open wheeler

seeya out there soon, I hope

[pologti18t]

Have a look at the autospeed.com site. Julian has done a few stories on aerodynamics. He has a Skoda Roomster and sometimes posts in that forum.

His aim was for improve economy though
AutoSpeed - Trialling a Rear Undertray
AutoSpeed - Modifying Under-Car Airflow, Part 1
AutoSpeed - Modifying Under-Car Airflow, Part 2
AutoSpeed - Reducing the drag on square-back cars

[blackbetty]

Have a look at the autospeed.com site. Julian has done a few stories on aerodynamics. He has a Skoda Roomster and sometimes posts in that forum.

His aim was for improve economy though
AutoSpeed - Trialling a Rear Undertray
AutoSpeed - Modifying Under-Car Airflow, Part 1
AutoSpeed - Modifying Under-Car Airflow, Part 2
AutoSpeed - Reducing the drag on square-back cars

As i have a huge interest in land speed racing (i especially hope that they can approve racing on lake Omeo in country Vic) i very much enjoyed reading these articles, thanks for posting the links.

I have articles at home on aero tricks for cars - i'll try to go through them on the weekend and find some relevant stuff for this thread.

As the GTI is a hatch the sudden drop ver the rear window is probably the single biggest area to make aero gains. the undertray would be second (mainly because of the tray thats already there from the front bumper). the polo bluemotion (not sure if that was the model name) also had some good areo ideas

[VWindahouse]

Very true. Here is a link to some wind tunnel testing for the Bluemotion 9n testing.

POLO BM IN THE WIND TUNNEL - YouTube

[blackbetty]

i did some reading up on the weekend about undertrays and general aero tricks. to make a one piece under body tray i reckon is over kill. the general consensus is to tackle individual sections such as a cover for the rear suspension, the rear boot - spare wheel - fuel tank etc. this is a very (time) expensive experiment. but it would be easier if tackels with a section at a time.

some general tricks to improving your top speed (and i mean top speed only):
keep the front of the car as close to the ground as possible (street cars obviously cant do this) - front air dams, fron wing extensions etc
wheel discs - but this will mean ur brakes get very hot
cover anything that could couse drag - the grill is prob a big improvement area. enough air enters below the number plate for cooling, so you could block the grill off totally BUT please keep an eye on your temp gauge
give the car a slight rake (rear end higher)
vent the pressure that builds up in the engine bay - that could mean a couple of lovers in the bonnet, or even lifting the rear of it up in relation to the front just enough to allow the air to get out. venting the hot air also helps with natural airflow passing through the radiator so in effect helps with cooling.
remove anything you dont need that could cause drag - wipers, mirrors, badges.
Tape up any seams Mcgyver style.
Keep the car very clean and waxed (NASCAR have proved a cars top speed is best when the cars are spotless, something like 3 to 5 MPH at 180+ MPH).

Also, keep in mind that HP and top speed is a "to the power of 3 factor"...for example lets say it takes 100 HP to go 100 KPH, then it would take 400 HP to go 200 KPH, 800 HP to go 300 KPH. So to improve drag/airflow even a tiny bit to gain that little bit extra top speed, is heaps cheaper (and more reliable) than pulling the extra HP.

to illustrate, my torana with a stock 179 six cylnder had a top speed of 145-146kph with a 3.36 diff gear and 3 speed automatic (super high tech stuff haa haa). after some of the aero cheats above (the single biggest gain was in grille and headlight covers), the car just touched the max of 160 on the speedo. But you cant drive around with a blocked off grille on a 40 deg day.
Plus it looked sh*t.