On boost, seriously, there is many websites describing how it works in effectively increasing the engine swept capacity at say one bar(14.4psi) a turbo engine is effectively burning as much air and fuel as an engine double its size.
Turbo efficiency comes into play. If you have an 740t with a stock turbo and intercooler, you will be exceeding the turbo compressor map ability by 12psi at the turbo and most boost gauges see it at the intake that we see. The job of an intercooler is to get that temperature down to reduce detonation, and reducing heat soak in the intake system from the hot compressed air. So upgrading the intercooler to a thicket one that isn't leaking as all stock ones do with increased boost do, is the first step you take.
This allows you to run the 12psi at the manifold on a stock turbo on overboost and run a little more ignition timing. From there, fuelling is more important.
There is a reason not many people use water/methanol injection anymore.
"The evaporative effects of the water, plus the octane boost of methanol, allows your motor to run more advanced ignition timing and/or boost to create additional horsepower with proper tuning. A general rule of thumb is that an engine will output one percent more horsepower for every 10 degrees intake temperature is decreased. Many enthusiasts have found the benefits of using water/methanol injection equivalent to running race gas, but without the $12/gallon price tag."
It's called e85, on a turbo motor it has more oxygen and a higher octane level. You need to install bigger injectors and fuel pumps and ideally install an aftermarket ecu. Something that means it's silly to bother with a little injector to put some water /methanol in a little squirter in your intake when you've just gone from 150rwkw to 200rwkws with a change of fuel, fuel pumps and ecu and tune. But you can drive the car hard all day long as long as there is fuel in the car. Unlike with a stock ecu with fixed ignition timing and fuel. Assuming you've already put a larger turbo on with better flow.
To do it on a non turbo 240 which works at peak ignition of about 16* and will ping on a b230 with 10:1 compression, but on any other motor is around 9.5 c.r, with fixed, non adjustable ignition timing and fixed fuel maps. Well, there isn't anything to cause pinging.
Not great reading, but this is on a tuned turbo car in the states
http://www.superstreetonline.com/how-to/engine/impp-1101-water-methanol-injection/
Keep in mind, we have much higher quality octane fuel as our top fuel than the Americans do and we run the Ron measurement system.