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Old 04-10-2008, 04:03 PM
  #1
TB993tt
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Default Aerodynamic musings

Being enthralled by Jussi's recent aerodynamic enhancements I have been pondering getting similar things done to my car.

My main dilemma is: is it a bit pointless since my car wears the GT2 arches ?

OK so I ain't going to get rid of the arches, no, they just look soooo bad, still love that fat *** look.

This got me wandering just how un-aerodynamic are the arches. The aerodynamics of the GT2 v the stock 993tt are quoted by Marc Bongers as:
993tt Cd 0.34 front area 1.93 CdA 0.656
GT2 Cd 0.34 front area 2.04 CdA 0.694

Now my arch kit is an FVD effort which is subtley different from the real GT2 kit. I had the arches fitted to cover precisely the set of genuine 993 GT2 Speedlines which I used to own.
So take a look at the Speedlines below on the real GT2 and see how they are tucked under the arches compared to my wheels (which are exactly the same sizes including offsets) it is obvious that the real GT2 is quite a bit wider....

To add to my confusion is the stated width of the real GT2 which is 1855mm - out came the tape measure and my width at the back is exactly 1855mm so the real stated number is correct to the edge of the wheels but not correct to the edge of the real arch since you can see below the real arches stick out quite a way from the the edge of the wheels.

So I am guessing that my arches are probably not quite the aerodynamic handicap that I thought, checkout how the front of my front arch don't flare as aggressively as the factory ones and how my resolved sill to rear arch is smooth compared to the factory arch "lip" stciking proud.

Just sharing some thoughts as I am trying to persuade myself to give the car some major surgery just need some encouragement


Last edited by TB993tt; 04-10-2008 at 04:31 PM.
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Old 04-10-2008, 04:11 PM
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ScottMellor
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Sorry Toby. I'm having a slow day. I'm abusing over-the-counter cold medication and could not resist.
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Old 04-10-2008, 04:41 PM
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With all due respect. Leave your car alone for God sake. It is one of the nicest looking 993tt/GT2s I have ever seen. IMHO. You want something with a lower Cd go drive your GT.
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Old 04-10-2008, 05:10 PM
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Toby, aren't the RSR flares slightly smaller than the GT2 Flares? Perhaps you have a copy of the RSR flares?
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Old 04-10-2008, 05:29 PM
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ca993twin
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Toby,
I echo the above... your car is a masterpiece. Would you draw a moustache on the Mona Lisa? Leave that amazing car alone.

BTW, I have always wondered if there really was an aero advantage to the shaved gutters (although they look bitchin')... since the rain gutters may act like small fences and keep the air on the roof from spilling over the sides. Or maybe not. Just thinking aloud.
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Old 04-10-2008, 05:58 PM
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I think that you should go for it.
I've been impressed with Jussi's developments and think that they could look good on your car.
The dp prototype also appears to have a flush rear screen which I think that you should go for as well.
The dp rear diffuser is interesting, I wonder if it works

Have fun.

Steve
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Old 04-10-2008, 06:44 PM
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In response to some communications from my bemused/confused Americano friends.
http://en.wikipedia.org/wiki/Anorak_(slang)
Sigh.
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Old 04-10-2008, 06:47 PM
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Thanks Scott... I had just assumed you had lost the last of your marbles. Very funny, and I'm afraid most of us on this forum qualify as anoraks.
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Old 04-10-2008, 07:30 PM
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Maybe the angle of the shot or different wheel camber makes the first picture look cooler, esp. the rear overhang. kaching!
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Old 04-10-2008, 07:54 PM
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Felix
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Toby - JFDI.
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Old 04-11-2008, 01:57 AM
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Jean
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TB

We've known you for a few years already and your madness only keeps growing, I think I am a t-shirt or sth. compared to you, but here we go, the better half saw me marking the floor and measuring the width and booked time at the shrink again, this is starting to be an expensive hobby.
Originally Posted by TB993tt View Post
This got me wandering just how un-aerodynamic are the arches. The aerodynamics of the GT2 v the stock 993tt are quoted by Marc Bongers as:
993tt Cd 0.34 front area 1.93 CdA 0.656
GT2 Cd 0.34 front area 2.04 CdA 0.694
[/IMG]
I always thought there is an error in this drag quoted number by Bongers and still do. I am convinced that the GT2 has more Area, more drag, and more downforce than the stock 993TT.

The measurements are as follows on my car:
Rear:
Width at the edge of the weels: 1960 mm
Width at the edge of the flares: 1990 mm approx.

Front:

Width at the edge of the weels: 1790mm
Width at the edge of the flares: 1850mm approx.

As to the front flares appearance (gap with the tires), on my car, some of it is due to camber

Measured the same way, my stock 993TT is:

Rear:
Width at the edge of the weels: 1780mm
Width at the edge of the flares: 1800mm approx.

Front:

Width at the edge of the weels: 1640 mm
Width at the edge of the flares: 1650 mm approx.
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Old 04-11-2008, 03:59 AM
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Toby,

You are a crazy man - But my type of crazy!

I personally LOVE the GT2 arches but am having troubles making them fit -they seem to be able to be mounted up and down the rear arches in so many ways......

As for the rain gutters - I agree with OFE - but i vote for structural integrity and A-Pilar fairings form Ruf instead.

Why do you always have to step it up a notch?

Simon.
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Old 04-11-2008, 04:05 AM
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Maybe the longer and more sloped windscreen could decrease the intimate feeling of the 993 with its small cabin. Or maybe you just feel better because of more room inside the car?

TB, how much seconds or meters do you expect to cut-off of your daily 0-250kph work trip exercise?
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Old 04-11-2008, 07:01 AM
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TB993tt
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Guys, thanks for the replies......

Scott
This IS a 993tt anorak forum you know, if I tried mentioning any of this to anyone outside these pages........ my cred would be destroyed.

Melman
The CGT has a much HIGHER Cd than the 993tt you know

Geoffrey
I think you are right probably - FVD designed this kit to work with the new sills.

Simon
Yup, it seems the arches can go in many positions - mine were matched with the GT2 Speedlines in situ.

Steve
Aero effect of gutter removal is unknown but all the fastest 911s had it done - and it does look 'kin cool

sfl993t4
It is Jussi's fault...... That diffuser would melt under our cars.

Phelix
You're bad...

Stummel
I always observe local speed limits

Jean
At last some real anorak stuff.....
Thanks for doing the measuring, the data is very interesting. Your EVO arches are as expected - wide.
The interesting one for me is the stock bodied width at the rear of 1800mm to the arches - this means mine is only 27mm wider each side which is not so much - I will check the front later.
I agree about the Bongers figures - there is no way a GT2 has the same Cd as a stock 993tt.
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Old 04-11-2008, 09:38 AM
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Don't do it Toby! As others have said your beautiful GT2 is an inspiration, a hallmark car. One of the reasons I bought a 993 was because of yours' and Jeans' rolling artworks. Having done a fair amount of autobody repair in the past, I dread any unnecessary metal work and paint blending. I can almost always pick it out because I have learned to look for flaws.
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