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Author Topic: Black magic Mk5 GTI track car  (Read 99214 times)

Offline the bruce

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Re: Black magic Mk5 GTI
« Reply #90 on: January 07, 2012, 10:28:19 pm »
Great posting, Fuscobal !! Like things like that.  :happy2:  :happy2:

I didn't recalculate that of course, but I'm sure you're on the right way.

These points are the ones I'd have told you if didn't wrote it by yourself:

4) I didn't also account for the chassis body roll and different tire loads.
5) I didn't take into account the effect of the greater corner exit speed on straights
 wich would bring time improvement on straights also (maybe another 1sec even !!!)

The body roll and suspension + tyre flex will cost you a second, the in-
creased corner exit speeds will give you the same the same second back.

 :wink:



ps:
I forgot to answer your question about the effect of a lowered car. Unless
don't have numbers I guess lift will be reduced by between 10 - 20 % or
somewhere about 50 N. So lift on front is almost zero and rear ~ 30 kg
@ 200 km/h.

pps:
Fuscobal, there is something irritating me:  :laugh:
Aerodynamic engineers talk about ''lift'' (positive numbers). If there's downforce
theses number are negative, cos it's just negative lift. It's because aerodynamics
mainly is to built planes, not cars.
I know racing engineers talk about downforce, so little confusing.
"You get what you pay for."

Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #91 on: January 08, 2012, 01:56:52 am »
Yes, the guys from Reverie are also talking negative numbers. For example here's a comparison between a 997 GT3 RS vs Reverie modified GT3 RS vs GT3 Cup racing car

http://www.reverie.ltd.uk/Downloads/ReveriePorscheData.pdf

1) I don't understand why the stock values of the GT3 are so small > at 160kmh, the front Df is 0.345kg and rear is 2.446kg (only this from that large OEm GT3 wing ???). Reverie gets it to a maximum of 10.272kg front and 13.695kg rear wich is much more but still to little as compared to what I've added into my calculation. The GT3 cup has -18.587 front (lift !!!) and 72.145kg rear. It's a little confusing why Porsche goes with small Df front and much bigger rear while Reverie gets them close to each other.
2) Also confusing why the CUP racing car has lift on front !
3) Another weird stuff would be why between the 2 Reverie versions with different riding height, the higher car has more downforce !? I thought it should be otherwise !

PS : Where do they measure the riding height ?  
« Last Edit: January 08, 2012, 01:58:53 am by fuscobal »
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Offline the bruce

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Re: Black magic Mk5 GTI
« Reply #92 on: January 08, 2012, 12:42:26 pm »
1. Have a look at some former SportAuto magazines.
In their 'SuperTests' they use have the cars in a wind tunnel.
I'm sure Porsche tries to get a good balance and low drag for
higher maximum speed.

2. Also balance. Cup cars have high camber for less understeer
in narrow corner. This may give dangerous high speed oversteer
if you don't have lots of rear Downforce.

3. If you have very flat underbottom (which even a stock GT3 has)
some amount of travelling air is needed for maximum Df .


997 II GT3:



Während der Vorgänger mit einer ausgewogenen Balance auf neutraler Nullebene vorstellig wurde, also bar jeglichen Auf- beziehungsweise Abtriebs, wird dessen Nachfolger nunmehr mit 152 Newton Abtrieb an der Vorderachse und gar 186 Newton Abtrieb an der Hinterachse bedacht.





http://www.sportauto-online.de/bilder/porsche-911-gt3-im-supertest-neuer-strassensportler-setzt-bestmarke-1332080.html?fotoshow_item=15#fotoshow_item=16


2006 GT3:







2007 comparison GT3 vs GT3 RS:

http://www.sportauto-online.de/supertest/datenanalyse-porsche-911-gt3-gt3-rs-im-supertest-besser-denn-je-der-neue-porsche-gt3-1345012.html




2007 GT3 RS:

http://www.sportauto-online.de/bilder/porsche-911-gt3-rs-auf-der-nordschleife-und-dem-hockenheimring-1041046.html?fotoshow_item=10#fotoshow_item=11



Rear Df of 100 N > 10 kg.


2011 GT3 RS:





Während der Mercedes-Windkanal an der Vorderachse bei 200 km/h noch etwa denselben Abtrieb wie beim GT3 ausweist (11 Kilogramm), fällt er an der Hinterachse deutlich höher aus: Dank des vom RSR abgeguckten Heckflügels wird sie mit 49 Kilogramm beaufschlagt (GT3: 19 kg). Das durch das verstellbare Karbonteil generierte, leichte Aufnickmoment nimmt der auch stärker ausgeprägteren Frontlippe des RS folglich etwas die Wirkung.






A 911 GT3 is a different thing than a Golf though. Completly different weight balance,
different suspension, much lower center of gravity and more ower though. Hope this
just helps for a better understanding.
« Last Edit: January 08, 2012, 12:46:02 pm by the bruce »
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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #93 on: January 08, 2012, 01:17:18 pm »
Yes Bruce, I've found a thread on Vagoc with much more tests done by these guys on many cars, among them some FWD like Cooper S or Focus RS wich varied a lot between each other also. Of course a Golf would be much more different than a 911 GT3 but perhaps I should talk to Simon McBeath at ''the wing shp'' . Here's what they say on their website :

Wing selection
If you require advice selecting the correct wing configuration(s) for your competition car, it will help us if you can tell us the following;

what type of events you compete in

what type of car you drive (saloon, sports racer, single seater etc). If you happen to have a reliable figure for the drag coefficient, that would be very useful! A photograph would help if you don’t have a Cd figure

what the car’s frontal area is (height and width plus a photo will just about do, but see the graphics below right for how to estimate it).
what your car’s power output at the driven wheels is (a flywheel figure will do - it is possible to estimate the at-the-wheels figure from this)
what the highest and lowest maximum speeds are at any venues you visit, and an idea of the cornering speed range encountered
what relevant regulations are applicable relating to the dimensions and location of wings and other aero devices
what deficiencies you are endeavouring to overcome
We then recommend the configuration best suited to your application. Fine tuning in testing and events will, however, be necessary to get a good balance.


Based on the data sent by me, he can make a profile in CAD/CFD for my car and recommend a proper downforce balance front to rear !
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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #94 on: February 01, 2012, 09:59:56 pm »
Weight deducted until now :

- subwoofer + enclosure > 34.5Kg
- spare wheel + tools > 17.5Kg
- MDF board over the amps > 8.2Kg
- Rear seats > 27.5Kg
- Front reinforcing bar > 1.8Kg
- S3 hubs > 3Kg
- Braking system > 12Kg
- 18'' wheels > 2Kg
- Recaro seats > 18Kg
- Lower rear bench > 5Kg
- Sinfoni amplifiers > 25Kg
- Rear seatbelts > 2Kg
- Odyssey ER40 battery > 15Kg

TOTAL until now : 171.5Kg





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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #95 on: February 08, 2012, 01:12:29 pm »
The VwRacing air-dam is here. Its weight including the mounting hardware is about 2Kg and I hope it will bring at least 10Kg of downforce on front axle !From the OEm front spoiler, this add-on lowers the car by 13cm on the edges(near the front wheels), 10.5cm on the front corners under the fog grills and 7.5cm on the middle. I will soon measure the OEm add-on to see the difference ! It is made out of very strong plastic (2mm) and reinforced on the middle section (5mm) !



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« Last Edit: February 08, 2012, 01:31:38 pm by fuscobal »
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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #96 on: February 08, 2012, 01:14:49 pm »

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« Last Edit: February 08, 2012, 01:16:33 pm by fuscobal »
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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #97 on: February 08, 2012, 01:24:34 pm »

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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #98 on: February 08, 2012, 01:25:47 pm »

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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #99 on: February 08, 2012, 01:27:08 pm »

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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #100 on: February 08, 2012, 01:28:20 pm »

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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #101 on: February 08, 2012, 01:29:17 pm »

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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #102 on: February 08, 2012, 01:37:11 pm »

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Offline the bruce

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Re: Black magic Mk5 GTI
« Reply #103 on: February 08, 2012, 03:00:54 pm »
 :happy2: :happy2: :happy2:

Guess that's more than enough DF on front.
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Offline fuscobal

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Re: Black magic Mk5 GTI
« Reply #104 on: February 09, 2012, 01:46:00 am »
Do you think it will bring some 10Kgs of downforce Bruce ? Also, I'm also hoping in a reduction of drag because the shape of the air-dam seems to deflect air from the front wheels  :smiley:
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