Thanks for this, John.
I'm confused on one thing though (being a bear of very little brain) - how can my MAF not be scaled? If it's sitting in a tube that's larger than it was designed for, surely more grams of air are actually going through the tube than would be in a smaller diameter tube (where it reads correctly)
If you're running revo BT, it's based on a code that uses a larger maf, ie cupra r or tt etc. They have basically the same ecu, so it's easier for tuners to start with a code that uses the hardware (as far as possible) that the car has on it.
The only difference between the cupra maf and the cupra R maf is the plastic tube around the sensor, so you effectively have a cupra R maf, and the code is written for it
The water has two effects in WI. Firstly some of it evaporates, and reduces charge temperature, helping density recovery. In the time available only so much can be evaporated, and if you intake temps are already low, the amount of water vapor the air can carry is relatively low.
The residual water has a second effect in that it slows down the flame front speed, but it also reduces flame temperature, and absorbs energy. There's a fine balance between slowing the flame front, and quenching it completely, It also absorbs energy that could be used to increase cylinder pressure, and do useful work on the piston.