If I have an EFI machine, and buy aftermarket addons such as intake and exhaust, there is no carb to rejet so do I just plug and play or does something need to be done to the EFI? Or does the EFI just compensate automatically? Thanks.

 

EFI is designed to compensate for altitude and temperature, if you just replaced the stock air filter with an aftermarket filter,without modding the lid or adding holes, it should be fine. Some are set up to handle aftermarket exhaust if the ECU is "told" it has to add fuel. A lot of the time, you need to buy an aftermarket "fuel commander" that will remap the fuel output to match your mods.