How do you figure that? I am not sure this formula would work, your assuming that everything is linear. Using linear momentum would get you close but than again even that will not work in this environment. A hand held radar pointed in a straight line at the moving vehicle is going to be the most accurate way to measure your speed. A dyno will not work due to it not being able to figure in environmental effects of humidity, resistance, aerodynamics, etc.
2002 330Ci Top Speed ?
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This is way to easy for mythbusters. You are making things way too complicated Big Daddy. Sure, there will always be variables that will slightly effect the outcome. Tires are a good example. As they wear out the diameter decreases which will slightly decease top speed. That does not mean that the method that I described will not yield a close estimate of your theoretical top speed and its easy to test since it works for each and every gear. If your redline is at 6000 rpm and your car goes 30 mph at 3000 rpm in 2nd gear, then your car will go 60 mph at 6000 rpm in 2nd gear, and so on. One other thing to remember is that in order for you to reach your top speed in 5th or 6th gear you might need a whole lot of pavement. The race track in Utah where the land speed records have been set it 10 miles long.
You have Zero wind resistance on a dyno, and that is the biggest non mechanical factor involved in top speed. Aerodynamics is not a consideration with a Dyno, so how can it tell your true top speed? The local track where I tested, taught and practiced High Performance Driving had a 1.1 mile straight and you could easily get to your "top speed". The race track in Utah is not really a race track it is a test track, and the 10 mile length is for setting land speed records in excess of 300+ mph, it is not necessary for achieving a top speed in a street car. The speedway is marked out by the Utah State Highway Department at the start of each summer. Usually two tracks are prepared; a 10 mile long straightway for speed trials and an oval or circular track for distance runs, which is typically between 10 and 12 miles (16 and 19 km) long depending on the condition of the salt surface. In recent years, there has also been a 5 mile (8 km) long straightway for qualifying slower vehicles. I will give your method a test this summer when I get back on the track and let you know what I find out!
iI believe that there is a govenor on the US BMW's to limit the top speed to be that of 135 mph. I got my 2000 328i up to thatpeed and then with more tach to go ( i wasn't @ redline) its like the car just would'nt go any faster. I checked on this and someone said that there are govenor's limiting the top end speed.