Originally Posted by Rick Carter

Originally Posted by 89FrontPorsche

You need to do something to counteract the natural tendency of the shape of the car to produce lift. Bernoulli's prinicple is involved here and when air travels over the top of a wing, the air underneath flows in a straight line. The air over the top must travel faster to meet the air at the bottom and therefore creates a low-pressure area. This is why a wing works and why your car, or most any car with nice, flowing shape like the 928 has, needs something to push the car down onto the ground, which is why you felt it "go light" at higher speeds which also results in less traction, among other things.

An S4 spoiler would be helpful, even going so far as to put some additional negative pitch to it. That means putting some angular shims between the wing and the car. Through-drill them so you can experiment.

The downside is that there has to be a compromise between downforce and aerodynamic drag. Too much wing angle and it robs the car of the ability to go faster. You probably already know this.

Additionally, the rear isn't the only thing to worry about. The front of the car is lifting up too and affecting steering. The speeds you were traveling at are higher than what it takes to get a multi-ton airliner off the ground. Most airliners rotate the nose high at around 150 knots which is about 172 mph. There is no doubt your car is creating lift but the spoilers are having some effect. I would not go much faster than 150 mph in a spoiler-less 928. Those Porsche engineers knew what they were doing. The spoilers on your car are designed to be "satisfactory" to the factory design speed limits of the car.

Naturally you are exceeding those with the nitrous and thus, entering into race-car territory.

A more aggressive front spoiler to generate front-end downforce is needed as well as more downward "lift" at the rear. But the more downforce, the more aerodynamic drag at high speeds so it's an art as much as a science. But in clinical terms, it's called "induced drag" or drag due to lift.

Some people, and myself included, have taken model cars, put them in a homemade wind tunnel and experimented with the model on a kitchen scale to see how much downforce I could make. Those scales are available at cooking shops and are usually not too expensive.

Then, to make it even more interesting, I had gone so far as to put two scales side-by-side to see what happened front vs. rear.

It was all an academic exercise while attending an aeronautical college years ago. I got a "B". Was really angry for all the effort I had expended. Internet didn't exist yet and all my data was actual, calculated and charted.

The drag part of it is a little harder. You have to take a string and put the car on its wheels and I found they needed bearings...so it started getting involved but..with the air moving at a constant rate, I could use the string, run through small pullies and attached to the scale, would pull it down a certain amount.

Naturally, the larger and more aggressive spoilers I tried, the more drag.

It's not something everyone enjoys doing but since it was an exercise for a paper, I thought it all very enlightening.

You have entered into the world of aerodynamics, sir. Not the goofy, kid-racer with funky colors on the cars with fart exhausts type of wings, either. Serious stuff. Many F-1 racers typically blast down the straights at 2225 mph+ often limited by either the length of the straightaway or by regulation. But aerodynamics plays a HUGE part in it.

http://en.wikipedia.org/wiki/Formula_One_car

Be careful, m'lad. You are in dangerous territory. I wish you well and success. But do so in one-piece, please.

Originally Posted by Lizard931

I find it VERY disturbing that you will not tell us where this happened.

But maybe I am the only one who thinks your lack of willingness to disclose where it was done says that you were on public roads.

Originally Posted by bwmac

Congrats, very cool achievement

Due to the threads on different power adders. Why NOS rather then a SC or Turbo

Originally Posted by Brett928S2

Hi Rick

I "think" those figures are wrong as they do not take account of autobox drag losses....

I was actually expecting to have to run even higher revs at the time....

The revs and speed figures I gave are accurate ...the revs come from my Ecu and the speed from GPS...

I would think that any system must have a built in error, but not that much....



All the best Brett

Originally Posted by bwmac

The error is in tire slippage.
As the car gets light, and because the road is not perfectly level, as the car lifts up and the weight comes off the rear tires there actually loose traction and you get wheel spin.
So your tires are doing 210 or more and you are doing 208 or whatever depending on slippage.

Originally Posted by Nicole

That's pretty darn fast! Congratulations!

I'm glad that man and machine survived it unharmed.

Originally Posted by bwmac

The error is in tire slippage.As the car gets light, and because the road is not perfectly level, as the car lifts up and the weight comes off the rear tires there actually loose traction and you get wheel spin.
So your tires are doing 210 or more and you are doing 208 or whatever depending on slippage.

Originally Posted by Imo000

WELL DONE!








I have hard time beleving this. If the tires loose traction, the RPMS will shoot up, followed by tire smoke. They car would become extremly twitchy too.