This post is an edit of and edit of an edit so if you search this in 6 months time, only this first post will make sense, and maybe some of the later ones!
I just wanted to clear up the S3 top speed thing.
You can see the gear ratios in the picture below, they are for a standard S3 6 speed box.
If you remap with the major remappers, then your rev limit is raised to 7200rpm. I've not personally seen an S3 with anything above a 7500rpm limit as firstly with the turbo they have stopped producing torque by then, and also the S3 engine would start self destructing at anything above this.
I have however input the gearchange at 7200rpm to illustrate the maximum top speed attainable in 6th gear.
As you can see 7200 is not a very suitable point to be changing for the gearbox.
Due to the nature of the turbo, and looking at RR graphs, I would expect people to be changing gear at 6000rpm, and for the car to be dropping power thereafter.
As you can see, the maximum top speed attainable in an S3 with the standard gearbox is 181mph. I have assumed the 3.27 final drive, though this figure 'may' be wrong. Several sources have reported this or 3.32.
You cannot possibly go any faster than this, physics does not allow this to happen.
However, if you're looking at your speedometer, they can be up to 10% incorrect thus it may appear as if you are travelling at 200mph.
If you have a big turbo S3, your top speed will NOT increase unless your rev limit increases. You will however, reach that top speed a lot quicker.
Lets say you have new rods, pistons, rod bolts, the works. Then you might get 8000rpm which will give you a top speed of 201mph.
At the standard rev limit of 6500rpm you could feasibly attain 163mph.
However, none of the above number are correct until you consider horsepower. Given the K04 turbo, you would reasonably be able to expect 150mph from the car. (assuming a realistic 260Bhp)
There is quite a few people on this site quoting higher top speeds than physics actually allows, taking into account rev limit and engine power including one person even claiming 175mph!
We can work out the actual top speed of an S3 if we can get the information on frontal area, drag coeficient, rolling resistance and engine power.
However, we can assume a general rule that production cars with known top speeds are running a correct horsepower figure to get there.
To get over 170mph, almost every production car has close to or over 350Bhp, with the lowest horsepower figure I can think of to attain a genuine 170mph is a Porsche 911, a car with a far more aerodynamic profile, lower drag and a naturally aspirated engine.
This difference regarding N/A and a turbo car is important, as turbo engines tend to produce power very slowly after their midrange punch, and it takes a long time for power to develop higher in the rev range, whereas a N/A car will produce power right up to the redline.
As is discussed further down the page, power has to DRASTICALLY increase once you hit the aerodynamic wall to continue to go faster, and that aeordynamic stop is somewhere around 140mph onwards.
If anyone has some more information, like proper datalogs, not anecdotal evidence, it would be cool to get them in this thread...
EDITED TO REFLECT NEW INFORMATION ON FINAL DRIVE