No, heat doesn't create velocity. Heat creates volume. If you look at any of the physics laws for gasses, you will find that pressure and volume and heat are related. PV=NRT is a popular one, The V isn't for velocity, it is for Volume.
Hotter gasses have more volume, thus requiring a higher A/R which in effect means that it starts at say 3" and scrolls down to approximately 1". Lower temperature gasses are denser and have less volume, so they require a lower A/R housing which would start at the same 3" volume, as the turbine housings use standard flanges, and scroll down to say 3/4".
Think about it like this, put a pinwheel in a shell (to be like a turbo, or not) would the hot air make it spin faster if cold air is coming in the same volume? nooooooooo lol would a smaller volume of hot air moving fast or a large volume of air coming at a slightly slower but constant velocity move it more?
http://i.b5z.net/i/u/1473169/f...y.wmv
Modified by PantherRacer at 6:27 PM 3/7/2005