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996 Turbo - Stability at terminal speeds

lofi said:
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!
 
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
 
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 :)

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
 
Manic996t said:
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 said:
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 :)

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!
 
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.
 
Rob996.2cabrioTip said:
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.

To be fair, 150mph in a Cosworth is far more dramatic than 200Mph in a 911 :grin:
 
RWD_cossie_wil said:
To be fair, 150mph in a Cosworth is far more dramatic than 200Mph in a 911 :grin:

:yeah:

Even 100mph is :sad:

:thumb:
 
RWD_cossie_wil said:
Rob996.2cabrioTip said:
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.

To be fair, 150mph in a Cosworth is far more dramatic than 200Mph in a 911 :grin:

Thirded :grin:
 
911tom said:
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;



I bet his rectum opened like a set of theatre curtains!
 

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