Performance chips are integrated circuit chips that are installed on the vehicle's circuit board to modify the ECU settings. They are typically used to increase horsepower and torque and improve fuel efficiency. They are fairly affordable, easy to install, and easy to take off when needed.
Handheld programmers are small devices that plug into a vehicle's OBD-II port to modify the engine control unit (ECU) settings. They typically come preloaded with several tuning programs and can also be used to read and clear diagnostic trouble codes. These are some of the best car accessories to have in general which is why OBD-II handheld tuners are a really popular choice.
Piggyback ECUs are separate engine control units that work alongside the factory ECU to modify engine performance. They are usually installed in line with the factory wiring harness and can be used to adjust fuel and ignition timing.
Standalone ECUs are independent engine control units that replace the factory ECU. They are typically used for high-performance applications and allow for more advanced tuning capabilities. This will enable you to change almost everything possible but is also the most expensive and most challenging to do.
If the tune is too aggressive or not done properly, it can lead to engine knock, detonation, and other issues that can cause damage to the engine over time.
Additionally, tuning that modifies the engine beyond its limits or ignores manufacturer recommendations can potentially void the vehicle's warranty.