The basic principle of all chip tuning boxes is the same.
They manipulate the sensor signal going to the ECU, so the ECU compensates in a way which increases power.
In the case of chip tuning boxes for petrol turbo engines, the chip tuning boxes manipulate the pressure sensor signal going to the ECU
By telling the ECU that boost pressure is lower than the figure it should be, the engine increases boost pressure to the level it should be according to the table in its software.
This is the basic principle.
Depending on the engine, multiple boost pressure sensors may need to be manipulated in order for the ECU to increase the boost successfully.
On some cars intercepting one sensor is enough, on others, two sensors may need to be intercepted.
So how does the chip manufacturer know that the boost increase is safe?
They rely on the safety features built into the ECU of the car manufacturer.
Car manufacturers know that the sensors they fit are not 100% reliable and/or they could be damaged, one way or another.
The car manufacturer builds in safety features which will protect the engine if a sensor, or a number of sensors fail.
This is how the chip tuning box manufacturers design their products.
Car manufacturers build a certain amount of headroom into their engine, by headroom I mean extra power capability, chip tuning boxes exploit this headroom and the original ECU will highlight a problem if the chip tuning box is trying to do too much.
The MAF versus boost pressure signal is the most obvious example on a turbo petrol engine but modern cars also have very active knock and lambda sensors which give a very good idea of how the engine is behaving.
If the ECU is getting readings which do not fit into the knock/afr tables it has, then again, it will cause a check engine light and or limp mode.
And this is how the chip tuning boxes can operate on a modern engine safely.
The limits of chip tuning boxes.
The beauty of chip tuning boxes is that they are simple to connect and they can be disconnected from the car without leaving a trace, ie they do not change the factory fuel, knock, timing tables.
But this also places limits on how much power they can produce.
Fundamentally, without altering the values of the tables in the ECU, the chip tuning boxes will always be limited to what the ECU expects to see. For people who want to change turbos there are simply too many parameters that need to be altered for a chip tuning box to be effective on more than one vehicle.
Also, when it comes to fitting larger turbos, most likely the car will have other modifications such as downpipe, race cats, intakes etc etc. There are simple to many combinations for any chip tuning box manufacturer to cover in a cost effective way.
And this is where custom tunes or stand alone engine management comes in.
Because chip tuning box manufacturers know what spec the engine is in, and that the car manufacturer made all of the cars with the same size turbo, air filter, exhaust, cams etc, they can make a product with a big market.
When it comes to bigger turbos, there are too many possibilities of turbo size to cater for all customers, a custom tune is the most effective and cost effective solution.
Chip tuning boxes manipulate sensor readings to allow the engine to make more boost. The ECU will highlight a problem if the chip tuning box is trying to change the signals by too much ie the chip tuning box is pushing sensors values outside of what the ECU thinks is reasonable.
This one size fits all type of product is great for engines where there are tens of thousands on the market but when things start changing a custom tune or stand alone engine management is the more cost effective solution for the customer.
I am sure chip tuning box manufacturers could come up with a chip tuning box solution if they know the specs of the engine, but that chip tuning box would only be useful on that particular engine, the research costs would not be covered by the amount of units they could sell..
There is a place for chip tuning boxes, piggy back units, stand alone engine management and custom remaps. The correct choice for you comes down to the specification of your engine and if it is modified, how modified is it.
In the case of chip tuning boxes for turbo petrol engines, they are suited to cars which are close to standard which means original catalytic converter and original size turbo.