A Shift kit is an aftermarket component for automobiles to improve how well the car shifts between gears. Kits are made for both automatic and manual transmissions.
Manual transmission kitEdit
For manual transmission equipped cars, it is a component that replaces the stock gear selector (shifter). A shift kit usually shortens the throws of selecting a gear (also known as a short throw shift), therefore allowing a driver to reduce the shift time and change gears more efficiently.
Automatic transmission kitEdit
An automatic transmission's main focus is smooth shifting between gears. To accomplish this it often goes into two gears at once while shifting up, which is known as a shift overlap. In these cars, it is a kit that can reduce or eliminate the shift overlap. It will also reduce wear because the transmission won't be trying to drive in two gears at once.
Typically, adjusting the shift 'pattern' in an automatic gearbox involves interrupting the signal from the ECU to the transmission (usually with a switch, though the adjustment can be made permanent). The resultant shift pattern is usually very aggressive (it will 'bang in' to gear) thus making a car a handful in the wet as well as opening the possibility of damage to already weakened transmission internals.