>>364335503
Look at the power and moment graphs of your car.
You want to have the engine at maximum power and torque, to go fast.
See that bump in Power? You want to keep engine in that region.
 So don't let the RPM fall too much when switching gears, some cars loose power when RPM too high, and of course if there is no limiter you can literally explode your engine.
Be careful when downshifting, you can force your engine spin too fast and break it, downshift only at safe RPM.