Power gear
Some cars in stunts have the ability to reach a so-called 6th gear. This usually happens while driving in the last official gear with a high RPM, and doing a jump. Some cars can reach it from any speed, when driving on a loop, and shifting to the last gear.
6th gear allows cars to go a lot faster than the given maximum speed and more importantly not even slow down on grass, when driving in 6th gear. These are: Porsche March/INDY, Ferrari GTO, Corvette ZR1 and Acura NSX. The INDY and the Acura can reach power gear from any speed using a loop. The INDY, Ferrari and Corvette go 245 mph in 6th gear, while the Acura only goes 203 mph.
Finding the 6th gear spots on a competition track is the key to victory. 6th gear was officially confirmed by Stunts lead programmer Kevin Pickell as a programming bug.