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911tom
Barcelona


Joined: 22 May 2012
Posts: 1377
Location: Buckinghamshire


PostPosted: Thu Feb 16, 2017 1:02 pm    Post subject: 996 Turbo - Stability at terminal speeds Reply with quote

So my build is slowly ticking along and just as I think I am approaching the end there is yet more to think about and potentially spend money on.

Can anyone offer advise on improving stability. My car currently sits on standard B4's that have been on the car since new. My current plan is to go full ohlins ideally. This may be over the top. My car will never see the track in anger. That is not what this car is for. It is going to be used on the road and at runway style events where it will see 200MPH+. I need it to be as stable as possible and safe for all the obvious reasons. It could be ohlins are over the top for this purpose but with the cash I have spent so far I do not want to cut corners just to save a few quid.

I have had the car up to 191MPH GPS and it felt very stable. But Ken at 9e has mentioned so many times that this changes when you get to 215MPH.

My car currently sits on the standard turbo twists with standard tyres etc all as porsche intended. It is in standard form with no aero or GT2 body bits.

Can anyone advise whether it is worth going with ohlins?
Should the car sit slightly higher?
Any tricks with camber etc?
Should I be considering aero front splitter or GT2 kit to add some downforce etc?
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911tom
Barcelona


Joined: 22 May 2012
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Location: Buckinghamshire


PostPosted: Thu Feb 16, 2017 3:11 pm    Post subject: Reply with quote

I also better keep a check on tyres. I am sure sticking with N rated PS2's has got to be the safest thing to do to prevent this;


Open Youtube Page

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ragpicker
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Joined: 14 Apr 2013
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Location: North East England


PostPosted: Thu Feb 16, 2017 3:18 pm    Post subject: Reply with quote

911tom wrote:
I also better keep a check on tyres. I am sure sticking with N rated PS2's has got to be the safest thing to do to prevent this;


Open Youtube Page


I was expecting more drama than that, but pleased to see that if we get a blowout at massive speed that it should be controllable!

Surprised
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Gareth64
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Location: United Kingdom


PostPosted: Thu Feb 16, 2017 3:30 pm    Post subject: Reply with quote

Surprised Surprised Surprised Surprised Surprised

Agreed. I thought it'd be completely uncontrollable and involve sideways and backwards action at that speed...
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911tom
Barcelona


Joined: 22 May 2012
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Location: Buckinghamshire


PostPosted: Thu Feb 16, 2017 3:34 pm    Post subject: Reply with quote

Gareth64 wrote:
Surprised Surprised Surprised Surprised Surprised

Agreed. I thought it'd be completely uncontrollable and involve sideways and backwards action at that speed...


Yes that and a couple of barrel rolls! I think a lot of luck came in to play there.
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HSC911
Indianapolis


Joined: 23 Jul 2014
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PostPosted: Thu Feb 16, 2017 3:36 pm    Post subject: Reply with quote

Now that was a bit more tame then I expected

Try this for downforce:






Sad
 
  
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911tom
Barcelona


Joined: 22 May 2012
Posts: 1377
Location: Buckinghamshire


PostPosted: Thu Feb 16, 2017 3:42 pm    Post subject: Reply with quote

hsc911 wrote:
Now that was a bit more tame then I expected

Try this for downforce:






Sad




Oh lord what have they created! Problem is it will fall off at 80mph! Jin I am sure you can do me a full GT2 kit cheap enough, you must have the parts in your stores?
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HSC911
Indianapolis


Joined: 23 Jul 2014
Posts: 2300
Location: Bedford


PostPosted: Thu Feb 16, 2017 3:44 pm    Post subject: Reply with quote

911tom wrote:
Jin I am sure you can do me a full GT2 kit cheap enough, you must have the parts in your stores?


Very Happy

Nearly got a whole 996 GT2 in parts Floor

Thumb
 
  
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Robertb
Zolder


Joined: 01 Sep 2003
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Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Thu Feb 16, 2017 6:03 pm    Post subject: Reply with quote

911tom wrote:
Gareth64 wrote:
Surprised Surprised Surprised Surprised Surprised

Agreed. I thought it'd be completely uncontrollable and involve sideways and backwards action at that speed...


Yes that and a couple of barrel rolls! I think a lot of luck came in to play there.


Credit due to PSM I would say.
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Stubbsy996
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Joined: 10 Feb 2007
Posts: 41
Location: Essex


PostPosted: Thu Feb 16, 2017 7:04 pm    Post subject: Reply with quote

hsc911 wrote:
Now that was a bit more tame then I expected

Try this for downforce:





Now that just looks awful!
Sad
 
  
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MrB
Trainee


Joined: 10 Feb 2016
Posts: 55



PostPosted: Fri Feb 17, 2017 4:19 pm    Post subject: Re: 996 Turbo - Stability at terminal speeds Reply with quote

911tom wrote:

Can anyone advise whether it is worth going with ohlins?
Should the car sit slightly higher?
Any tricks with camber etc?
Should I be considering aero front splitter or GT2 kit to add some downforce etc?


Hi Tom, naturally there are far more knowledgable people on here than I, and I can't provide opinions on suspension set up... but I would hedge my bets that investing in better aero would be a wise investment at the speed ranges you're aiming for.

1. Potentially and most simply, you could consider something like the addition of an x50 aero kit, especially in reference to the deeper front splitter. Its quite a large appendage compared to our stock Turbo items and you know the factory obviously invested in developing the system.

2. Go for the GT2 bumper / aero / front rad system... I know (from my own experience on our modded Mk1 C2) that the addition of a custom CUP bumper, carbon radiator mounting system that canters the angle of the radiator and modified GT2 rad chimney, does add significant downforce and stability to the front end of a C2 when up in the higher speed ranges... especially when compared directly to my stock body C2.

Naturally you'd need to look to equalise the front / rear aero balance of downforce... but if your targets are in the big league of runway speed runs, I'd say this was a sensible upgrade.

I will add though... its a slippery and expensive slope if you're aiming to remain with OE parts... but you can't take money with you and it'll be a beast of a car! Thumb

MrB
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lofi
Suzuka


Joined: 08 Jun 2009
Posts: 1028
Location: Surrey/Kent border

2001 Porsche 996 Turbo

PostPosted: Fri Feb 17, 2017 4:27 pm    Post subject: Reply with quote

Worth a chat with centre gravity. When I spoke to them about high speed stability (my turbo seemed to be lacking - and we're talking normal speeds not 215) they immediately pointed to the rake of the car. These car tend to sag down at the rear. The change they made to get closer to factory rake was small but the difference it made to high speed stability was huge.
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911tom
Barcelona


Joined: 22 May 2012
Posts: 1377
Location: Buckinghamshire


PostPosted: Fri Feb 17, 2017 5:09 pm    Post subject: Reply with quote

MrB - Thank you for your comments. I agree Porsche will have invested a lot of time and cash in the design. Far more than anything aftermarket. But yes genuine GT2 parts are crazy money so I may have to wait a while before I commit to that

lofi - I am in talks with centre gravity now. I have a quote from them and they are very reasonable with their pricing and I have heard only good things. I have briefed them on my goals etc.

So centre gravity and definitely look at GT2 kit. thumbsup
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lofi
Suzuka


Joined: 08 Jun 2009
Posts: 1028
Location: Surrey/Kent border

2001 Porsche 996 Turbo

PostPosted: Sat Feb 18, 2017 12:02 am    Post subject: Reply with quote

I think you'll be in good hands at CG
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spiderlane
Spa-Francorchamps


Joined: 07 Feb 2015
Posts: 266
Location: The South East


PostPosted: Sat Feb 18, 2017 9:59 am    Post subject: Reply with quote

Agreed. I visited them a couple of weeks ago - everything good you read about them is true, well, it was for me. They'll get the car you want it.

Mark
 
  
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EGTE
Spa-Francorchamps


Joined: 06 Jul 2015
Posts: 339



PostPosted: Sat Feb 18, 2017 11:22 am    Post subject: Reply with quote

lofi wrote:
Worth a chat with centre gravity. When I spoke to them about high speed stability (my turbo seemed to be lacking - and we're talking normal speeds not 215) they immediately pointed to the rake of the car. These car tend to sag down at the rear. The change they made to get closer to factory rake was small but the difference it made to high speed stability was huge.


Spot-on; a car is effectively wing-shaped (especially a 911) and if the rear sags, it increases the angle-of-attack of that "wing", so you get more lift all speeds. So stance is actually a huge aerodynamic factor, as well as all the air dams/splitters and spoilers rightly mentioned elsewhere.

Aerodynamic effects increase as square-laws usually, so pushing a car beyond its design speed can rapidly become very interesting!
 
  
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Manic996t
Silverstone


Joined: 05 Jul 2015
Posts: 120



PostPosted: Sun Feb 19, 2017 10:01 pm    Post subject: Reply with quote

the 996t was designed to be neutral lift and low drag. It has inherent high speed stability, so is already perfect for vmax style events. However the original design intent was for circa 190 ish mph top speed.

how it behaves over 200mph i don't know, however their is a chap in the states who runs stock aero and runs in the region of 220mph in texas mile style events

GT2 aero will give you some great additional aero downforce but with the penalty of drag which doesn't really fit with your vmax application

Suspension may not seem important but what coilovers will give you is the ability to set the car up to compensate (to an extent) for the change in stability at 200mph+

where you need to be careful is when coming off the throttle at the end of a run as the rear end unloads it could cause the car to become unstable

I would personally have a full cage, bucket seat and harnesses fitted if you intend to go over 200 mph on a regular basis

and also you will need to manage tyres carefully
 
  
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Bodgerben
Trainee


Joined: 02 Jan 2012
Posts: 58
Location: Hants


PostPosted: Sun Feb 19, 2017 10:28 pm    Post subject: Reply with quote

Tom, you're doing the right thing visiting CG, Ken said to us that after removing the front diff, drive shafts etc and ditching the spare the rake is wrong. With your amount of power you need to make sure the rake is correct, Ohlins are the way to go.

Of course, the bodgers way is to put a couple of bags of sand in where the spare used to live to replicate the weight of the diff and drive shafts, rake back to how it should be Smile

HTH

TBH - Caroline's is running B6's and had new 030 springs, with RWD geo done by 9e (4/5 years ago) which has been great. We would go for Ohlin's now if and when we needed a refurb, no bags of sand needed (not that we've actually needed them).

Ben
 
  
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911tom
Barcelona


Joined: 22 May 2012
Posts: 1377
Location: Buckinghamshire


PostPosted: Mon Feb 20, 2017 1:08 pm    Post subject: Reply with quote

Manic996t wrote:
the 996t was designed to be neutral lift and low drag. It has inherent high speed stability, so is already perfect for vmax style events. However the original design intent was for circa 190 ish mph top speed.

how it behaves over 200mph i don't know, however their is a chap in the states who runs stock aero and runs in the region of 220mph in texas mile style events

GT2 aero will give you some great additional aero downforce but with the penalty of drag which doesn't really fit with your vmax application

Suspension may not seem important but what coilovers will give you is the ability to set the car up to compensate (to an extent) for the change in stability at 200mph+

where you need to be careful is when coming off the throttle at the end of a run as the rear end unloads it could cause the car to become unstable

I would personally have a full cage, bucket seat and harnesses fitted if you intend to go over 200 mph on a regular basis

and also you will need to manage tyres carefully


Thanks Umreet. I certainly do not intend on pushing it over 200mph very often. I like the cage look and GT3 seats but I am one of the few owners that uses the rear seats on a regular basis so they would be missed. I will discuss the aero with CG and see if they have an opinion. GT2 is probably the way to go and yes you are right about drag however if power can overcome this then I'd rather have better stability and safety. As I am not tracking the car ohlins are probably OTT in many ways but will offer additional adjustment etc.



Bodgerben wrote:
Tom, you're doing the right thing visiting CG, Ken said to us that after removing the front diff, drive shafts etc and ditching the spare the rake is wrong. With your amount of power you need to make sure the rake is correct, Ohlins are the way to go.

Of course, the bodgers way is to put a couple of bags of sand in where the spare used to live to replicate the weight of the diff and drive shafts, rake back to how it should be Smile

HTH

TBH - Caroline's is running B6's and had new 030 springs, with RWD geo done by 9e (4/5 years ago) which has been great. We would go for Ohlin's now if and when we needed a refurb, no bags of sand needed (not that we've actually needed them).

Ben


Thanks Ben. I certainly do not want to be ballasting the front 1960's style! Hopefully a correctly set up car with the 'rake' as you say corrected will be enough. If not then I'll have to go GT2 front and rear.

Does anyone know if the GT2 replica parts actually work as well as the real thing? Something like this from design911;

http://www.design911.co.uk/fu/prod128790/Design-Aerokit-Package--GT2-Porsche-996-08-2001--_2/

I guess it depends how well they have copied the original part.....

As we all know genuine GT2 parts are crazy money!
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Rob996.2cabrioTip
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PostPosted: Mon Feb 20, 2017 1:41 pm    Post subject: Reply with quote

i had a similar, although lower speed (150ish)/spec blowout. i had a 350bhp 4x4 cosworth suffer a rear tyre failure and apart from the rumble is was pretty un dramatic. obviously at that speed the rim needed replacement.
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