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997GT2 rear sway bar is 25.5mm - 997GT3 rear sway is 23.9mm (discuss)...

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997GT2 rear sway bar is 25.5mm - 997GT3 rear sway is 23.9mm (discuss)...

 
Old 02-04-2008, 12:31 PM
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997gt3north
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Default 997GT2 rear sway bar is 25.5mm - 997GT3 rear sway is 23.9mm (discuss)...

- both rear bars have 3 holes
- both bars are hollow
- i do not yet know what hole the GT2 arrives installed on
- the GT3 we know comes fully stiff

- is it stupid math to say that 1.6/23.9 (approx 7%) implies that the GT2's bar is 7% stiffer ( or do we use different math for twisting a hollow tube?)

- think i might give a sway bar company a phone call


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Old 02-04-2008, 12:37 PM
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gmg is making new sway bars that will be released in a few weeks. I'll let you know how they work as I am ordering them
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Old 02-04-2008, 01:30 PM
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Jean
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Originally Posted by 997gt3north View Post
- is it stupid math to say that 1.6/23.9 (approx 7%) implies that the GT2's bar is 7% stiffer ( or do we use different math for twisting a hollow tube?)
Same everything else, the stiffness of the GT2 bar is about 30% more than the GT3. I would be surprised if the lever arm length is the same as well.
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Old 02-04-2008, 01:36 PM
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There is a Porsche bulletin letting delaers know that the GT2 bar will fit a GT3 as they are anticipating people moving to it.
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Old 02-04-2008, 03:12 PM
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The Gt2 has a wider rear tire and more weight. Increasing the rear sway stiffness is needed to counter the increased understeer from the those 2 factors
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Old 02-04-2008, 03:37 PM
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Anyone know the part number?
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Old 02-04-2008, 03:45 PM
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997gt3north
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Originally Posted by 03-turbo911 View Post
Anyone know the part number?
Yes,

It is going on my as we speak.
If you are going to order the bar (it does fit) you also need to order 2 of the bushing as the bar is bigger (don't know those part numbers).

Part Number for the rear bar is 997.333.701.94

Last edited by 997gt3north; 02-04-2008 at 04:50 PM.
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Old 02-04-2008, 04:14 PM
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My rear bar came from the factory in the middle setting. Are you guys running it in the full tight setting? What effects would changing the setting make?

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Old 02-04-2008, 04:30 PM
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The part number for the bushes is 997.333.792.94 and you need two.

The new bar is 20% stiffer on the middle setting than the original bar on the stiffest setting.
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Old 02-04-2008, 05:18 PM
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997gt3north
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Update, just found a formula to calulate stiffness for sway bars

link below
http://www.kormanfastbmw.com/tantiswa.htm

basically it is:

% increase in anti-sway bar stiffness = (new diameter / old diameter) ^ 4

therefore, gt2 bar at 25.5mm and gt3 bar at 23.9mm => (25.5/23.9)^4 = 1.295

therefore it would appear to be 29.5% stiffer of a bar

therefore, Scott's statement that the middle hole is 20% stiffer that the gt3's stiffest setting is likely correct / logical

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Old 02-04-2008, 05:39 PM
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assuming both have the same wall thickness.
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Old 02-04-2008, 05:48 PM
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Originally Posted by flash1034 View Post
My rear bar came from the factory in the middle setting. Are you guys running it in the full tight setting? What effects would changing the setting make?

Flash
I think the rear bar is much better in the middle setting on the 997 GT3. My GT3 was very "twitchy" when the rear bar was on the full stiff setting. The stiff setting appears to be better for the RS, probably because the RS has a wider rear track and more inherent understeer. IMHO
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Old 02-04-2008, 09:59 PM
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IMHO stiffer is better. The car understeers a lot even in the stiff setting. I would love to try the gt2 sway bar.

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Old 02-04-2008, 11:40 PM
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Jean
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Originally Posted by Jean View Post
Same everything else, the stiffness of the GT2 bar is about 30% more than the GT3. I would be surprised if the lever arm length is the same as well.
Was my post invisible?
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Old 02-05-2008, 01:27 AM
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997gt3north and ScottL, thank you both for the part numbers. I'll order it this week and will probably stick with the second hole.

Jean, you aircooled guys get no respect lol
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