jason latif

...I need some recommendations as to how to improve the high speed stability of my 996 C4.

It's a '99 model (I think 2001 brought in better downforce characteristics) and yesterday I was on the highway at approx 90mph, with occasional 70mph cross-wind gusts.

Even without the gusts, my car felt a little 'floaty' (although it's got the sports suspension) and with the winds, the car was being pushed all over the place.

The car is a stock C4 in terms of body - so would one of the body kit upgrades help (either Porsche or after-market). I'd only go down this route if the front dams/ spoilers etc. significantly reduced lift at high speed - I'm not bothered about looks (as I like the stock look anyway).

All comments appreciated.

[Getting the Porsche Sports Exhaust fitted this week !!] <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

FixedWing

I'm a little surprised at your complaint.

I am always driving my 996 Turbo on the highway at 200-230 km/h with strong cross winds (and faster in calm air).

Any car will react to a cross wind. How can it not? But the important thing is whether or not it is inherently stable. You want the car to move in such a way that it tends to want to re-center itself instead of get further out of track. I find the Turbo very good at this. Yes, it moves around but as soon as the gust stops it is headed back into lane. Other cars might weathervane and then you really need to fight them to keep them where you want them.

One thing I have noticed with the Turbo though is if the wind is strong enough it can mess up the airflow under the car. This makes it feel a little strange. But that is a very strong wind.

I don't think you can expect the car to stay absolutely planted. Any car will move about under you if the outside conditions are changing. Maybe drive more aggressively? Sometimes I find that if I am driving very easily the car doesn't feel good but when I push hard it is very communicative and seems to react better. I think it is an emotional thing. So try driving through that feeling and see how you feel about the car then.

S.

Sloth

[quote]Originally posted by jason latif:
<strong>...I need some recommendations as to how to improve the high speed stability of my 996 C4.

It's a '99 model (I think 2001 brought in better downforce characteristics) and yesterday I was on the highway at approx 90mph, with occasional 70mph cross-wind gusts.

</strong><hr></blockquote>

I imagine any car would feel a little unstable with near hurricane force cross winds of 70mph. No wing or body kit would help with that.

As far as I know the bodies are identical from the 99 model till it was freshened for the 2002 year.

Andreas.

I'm also a bit surprised, mine is also a '99 model, and i don't feel my 911 "floating"..

If you're in Europe (..Km/h) this weekend was very windy, about more than 140Km/h in some places...so maybe that could explain your experience..!

Armando Ramirez

There is a reason Porsche put the areo kit on the GT3!!!!!!!!!!!!

I would expect any car to act strange in a 70mph cross wind...geezzzz driving inside of twisters are we???



If your not used to driving in the over 100MPH range you will feel the car as twitchy....that is just becasue everything is going on much faster and it takes much less effort to trasnfer weight.

I've got the areo kit, and I can feel the car hunker down as it goes over 120...at road atlanta and vir where you get some nice top ends you can actually see (mostly feel) the car compress downward and become even more stable/planted.

Is it on one streach of road you get this feeling or just in general? You could be on a road with a bad crown which at high speed will make the car drift off the road faster. or you might have too much toe out in your alignment. This is great for turn-in very nice but make the car very twitchy at higher speeds. Might even be air preasures off too much on either end will give you a weird feeling at high speeds. Worse case its your tires and you could have a belt going. Not knowing what exactly your feeling makes it tough to tell. I have been in a LOT of 996's on the track and none of them felt "light" on the track at speed. I know light...I used to drive an 88 Targa...that got light after 130...very light in the front...

A little more feed-back on the feeling and maybe we can help you figure it out...

Hope this maybe Helped???

SpectraG

I have a 2000 996 C2 with GT3 kit and 19inch wheels on.. i've been driven my car over 165 miles several times, its quite stable.. and ppl who have sat in my car all felt that the ride is quite safe and doesnt feel like its going that fast..

JasonAndreas

The purists will bitch & moan about "how it was meant to be" but the only way to fix your problem is with a big *** wing. Adding a front spoiler will help a little bit, adding a rear wing will make an enormous difference. Lowering an older 964-993 porsche would help but if you couldn't tell the difference between a car with a rear undertray from one that had it removed, chances are, you lowering it would do nothing for your confidence. In my very limited experience, the 996 behaves the exact same way. Chances are you'll start noticing a difference at 55-60mph. Stabbing the throttle for a few seconds so you can say you drove at a 140mph doesn't count. A porsche is more stable and a hell of a lot more comfortable to drive with an aero package.

jason andreas
1993 964RSA

993RS

This is from Paul Frere's "Porsche 911 Story":




The x axis is speed in meters per second (1 meter per second = 2.2 mph) and the y axis is Kiloponds (=2.2 pounds)

As you can see already around 80 mph the effect of the spoiler is evident.

JimB

I drive a non-areo kit 99 c2 almost exclusively on the track and frequently at Brainard where a 996 will break 150mph every lap. There is no question that, in stock form, the car moves around a little bit over 145 which is a little unsettling given that at BIR you are headed into a 140mph corner. High speed instability could certainly be due to alignment or tires or any number of other issues but the first place to look seems to be air passing under the car. The problem with my car, which is lowered, was solved by attaching a 4 inch, flexible plastic dam to the back edge of the nose. It's less than 1.5 inches off the ground and keeps the air out from under the car. This solved the problem and the car is now rock solid above 150. This is obviously not a solution for a street car but it does identify the problem.

As for adding a rear wing, I'm pretty sure that will make things worse but who knows? My wind tunnel is on the blink again.

Palting

I don't believe that the solution is adding wings and front spoiler. Granted, the following comments come from a 996 C4S owner, so take it for what its worth.

I've driven my car several times at 170+ mph. It is stable as a rock, and feels plastered to the pavement. What I would suggest is that you look for other things that might be causing the instability. In stock form, the 996 should NOT be unstable at speed. Adding wings and front spoiler will increase downforce, downforce that you shouldn't need if the car is working right. They will also increase you CF, slowing you down and decreasing your top speed.

First thing you should check for is tire imbalance, then alignment. Just prior to changing over to a new set of tires, I noticed that my car started to have a tendency to wander, and I would have to make continuous small corrections at speed. Fortunately, this wandering tendency did not increase as I increased speed. Now, with newly mounted and balanced tires, it is again straight as an arrow and stable as a rock. I'd better quit, otherwise I'll keep coming up with these stupid similes.