Sudden Instability at 150mph
Three Wheelin'
Joined: Mar 2003
Posts: 1,402
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From: New Jersey
Porsche went to extremes to make the entire underbody flat including the engine tray....Ferrari does the same thing starting I believe with the F355. I don't think that tray is there just to reduce sound...
Rennlist
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From: Chino hills, CA
The only place in Florida for a safe 150 mph run would be on the turn pike... hopefully you are not running at this speed on the Dolphin Exp way....
Ck your rear kinematic toe, if that's off you will have instability at high speeds. There are very few places that have the correct toe gauge to determine the correct adjustment. The only place in S. Florida that can do this right that I know of is Champion Porsche. As I also had a high speed instability problem prior and it turned out to be the kinematic toe. I have had my 993 up to 150 mph on the turn pike without the engine tray and didn't experienced any instability issues.
Ck your rear kinematic toe, if that's off you will have instability at high speeds. There are very few places that have the correct toe gauge to determine the correct adjustment. The only place in S. Florida that can do this right that I know of is Champion Porsche. As I also had a high speed instability problem prior and it turned out to be the kinematic toe. I have had my 993 up to 150 mph on the turn pike without the engine tray and didn't experienced any instability issues.
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From: Chino hills, CA
Originally Posted by andrew911
Porsche went to extremes to make the entire underbody flat including the engine tray....Ferrari does the same thing starting I believe with the F355. I don't think that tray is there just to reduce sound...
Well.... FWIW, the 996s don't have them......
Three Wheelin'
Joined: Mar 2003
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From: New Jersey
Originally Posted by Robin 993DX
Well.... FWIW, the 996s don't have them......
By the way, I'm a NJ guy so not as familiar with Fla, but how about Alligator Alley for a top speed run
Rennlist
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From: Chino hills, CA
The engine tray subject has been a heated debate over the years. Again several tell tail sign that convinces me that it was not installed for stability is non of the pre 964 911s have them and as soon as they went to the 996 Porsche got rid of them. Of course there is always the possibility of cut backs on design as they did with everything else on the 996. :P
Never been on the Alligator alley, I assume you are referring to the highway the crosses the state of Florida from East to west?
Never been on the Alligator alley, I assume you are referring to the highway the crosses the state of Florida from East to west?
Three Wheelin'
Joined: Mar 2003
Posts: 1,402
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From: New Jersey
Yes- Alligator Alley is the highway that's in lower Florida (I forget what the actual highway number is)- I drove it when I was down there on business on the East, and decided to visit my folks out on the West. I have never seen a road as straight, flat and long as that....you could take the new Bugatti up to 250MPH there...I hit the speed governer of about 115 on the rental car and held it there for a while....well, just below it as constantly hitting the governer is quite annoying
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Racer
Joined: May 2004
Posts: 370
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From: SF Bay Area
Originally Posted by Robin 993DX
Well.... FWIW, the 996s don't have them......
Here is a pic of the 996 plate (borrowed from Gert's web site):
Addicted Specialist
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From: So.CA
Originally Posted by andrew911
What we know is the tray is there to help aerodynamics....
Swiss noise regs. This is why Porsche added the tray with the 964. At that time, the swiss had the most strict regs on noise output. And IIRC, another one of their regs also prompted Porsche to go to different gear ratios ...the taller 6th that we owners of the g50/20 know and love
when the /21 was the preferable box. I wish this could be put to rest, but the "aero improvement" needs to be beaten down with a big stick ...whew, feel better now 
Back to the instability at 150mph, the most immediate things that come to mind are:
- tire pressures
- tread condition
- alignment (especially kinematic since so few shops even know what this is)
- suspension condition
- bushing condition
Porsche has been accustomed to testing at 'bahn speed" for decades. If you have instability at that speed AND are planning on actually running it at that speed, I'd check the aformentioned very closely before proceding.
Edward
Drifting
Joined: Aug 2005
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From: San Diego, CA
My car is all over the place at 150+ with or without the tray and that's because my stock suspension sucks big time.(original monroes @ 90K)
I'm having Bilstein HD's, aggressive springs (325lb front/450lb rear) and turbo sway bars installed on my car as I write this and I'm completely convinced that it will be rock solid at any speed when completed with a corner balance and lowering to RS + 5mm ride height.
ZP44
I'm having Bilstein HD's, aggressive springs (325lb front/450lb rear) and turbo sway bars installed on my car as I write this and I'm completely convinced that it will be rock solid at any speed when completed with a corner balance and lowering to RS + 5mm ride height.
ZP44
Thread Starter
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Joined: Sep 2005
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From: South Florida
Originally Posted by sidned
Chris,
Your avatar shows your car wearing a pretty big rear spoiler. Has this been balanced with a complimentary front spoiler/splitter?
Your avatar shows your car wearing a pretty big rear spoiler. Has this been balanced with a complimentary front spoiler/splitter?
with the tray on so it has nothing to do with any changes. Suspension and tires
are exactly the same.
I have taken the car to higher speeds without ever experiencing this.
I have had many individual emails from people who
are well respected in the professional racing circuit and they all said that
the 993 race cars don't have trays, so they don't think that it was the cause.
I have to say at this time that I it could have been a gust of wind.
I'll try it again and see if there is any difference. This time I'm prepared.
Thanks everybody for listing all the variables.
Chris
Thread Starter
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Joined: Sep 2005
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From: South Florida
HWY 27 has no side entrances for one very long section. We have radio contact with start and end
so no other cars in the area are on this road. This is a very well known test spot for everyone down here. Cars and bikes. Never had any problems.
so no other cars in the area are on this road. This is a very well known test spot for everyone down here. Cars and bikes. Never had any problems.
RL Community Team
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From: Seattle
Scott 1996 993c2,
I just noticed your avatar! That is the best.
Regarding Alligator Alley- That is not the place to do high-speed runs. They regularly hit eastern end with helicopters, planes and roadblocks. I mean, honest to God 15-police-car roadblocks. They have a couple of officers stand in the middle of the road and wave cars off to each of the officers who then write them up.
I hit a speedo-adjusted 165 in my Ruf-equipped 930 on that road and managed to not get caught. Dumbest thing I have ever done.
Another thing about Alligator Alley is the alligators! Hit even a small one at speed and it is all over. They love to sun themselves on the sides and middle of the highway.
Be safe and keep it on the track.
I just noticed your avatar! That is the best.
Regarding Alligator Alley- That is not the place to do high-speed runs. They regularly hit eastern end with helicopters, planes and roadblocks. I mean, honest to God 15-police-car roadblocks. They have a couple of officers stand in the middle of the road and wave cars off to each of the officers who then write them up.
I hit a speedo-adjusted 165 in my Ruf-equipped 930 on that road and managed to not get caught. Dumbest thing I have ever done.
Another thing about Alligator Alley is the alligators! Hit even a small one at speed and it is all over. They love to sun themselves on the sides and middle of the highway.
Be safe and keep it on the track.
Three Wheelin'
Joined: May 2005
Posts: 1,717
Likes: 27
From: oceanside, ca
Highway 27 reminds me of the santa cruz mountains in the bay area. The motorcycles are well organized. If there is a cop in the area, they give each other special hand signals to be ccol. I have also heard that there is a website where they can go that updates the highway with current conditions....
People used to flash lights to warn of the PD, now people want to see you get nailed. Thanks for the heads-up buddy!!!!
People used to flash lights to warn of the PD, now people want to see you get nailed. Thanks for the heads-up buddy!!!!