http://www.scriptasylum.com/rc_speed/top_speed.html
Use this and play around with different voltages, gearing, etc. Remember though, once you start pushing past 50+ mph the calculator won't be as accurate, since air resistance and friction become much more of a factor. It might only take a 50W increase to accelerate from 10mph to 20mph, but to accelerate from 60mph to 70mph it might take 250W. Both increases are 10mph, but the one at higher speed takes 5x as much power. I just made those numbers up as an example so they aren't accurate, but the principles hold true.
EDIT: If you are going to go for the 1/10 scale make sure you have a very smooth strip of road to run on. As seen in the videos you can get a 1/10 going that fast, but like Linc said the 1/8 will be more forgiving to any imperfections in the road, and the 1/8 metal-gear drivetrain is more robust.
Hybrid Mode
