Powerbox is an additional electronic module that is bet in the original vehicle wiring. Usually it has a plug and socket, so after releasing the original wiring is it simply pushed into the original lines without soldering. Works by modifying the signals from the sensors. For example, if is the pressure in the suction 2300mBar, after embedded PowerBox, ECU receives a signal that is 2100mBar. Then it leads the ECU wants to increase pressure by 200mBar more. Here the real pressure will be the 2500 mBar. In a similar way powerbox is "lying" ECU on other values. The most common PowerBox with common-rail engine is based on rail pressure increasing (fuel pressure). With an unchanged duration of injection and higher injection pressure, through the nozzle there is flowing more fuel and the performance is increassed. Without adequate air added, EGT (exhaust gas temperature) and temperature of the combustion chamber rise and smoke how ever. And because the ECU does not know that it injects more fuel than it "thinks", detail of the trip computer consumption will be lower. Higher pressure in the rail increases the CR pump and nozzles wear. This type of powerbox (rail pressure increasing) is for example Novitec Power-rail.
The most primitive powerboxes (picture) contain only a few resistors and semiconductors, the most sophisticated they have their own maps, which lie to ECU according to algorhytm. They achieve good performance without smoke. They are such types, which are inserted between the main harness and ECU, they modify signals from all sensors. Such as the type Novitec Power-Jet. PowerBox advantage is ease of installation with a modern and nice performance boost. In addition, the manufacturers boast by the using of PowerBox you don´t risk the lose of warranty. This is misleading because the lose warranty is not only when the powerbox is removed before reparation, and its presence before the disturbance is concealed. The cons are: suboptimal operation of the engine, often high-wear performance, the increase of the power compared to the ECU mapping debugging is much lower. Another disadvantage is misleading indication of the board computer to consumption, which can be reduced by up to 2l/100km like reality. Powerbox from unknown manufacturers usually are set outside the safe range for the engine. Even some of the renowned manufacturers offer products that are not safe!