yes i forgot about water injection, ive found this which im going to have a go at, only trouble will be sourcing the jet as i cant find anything on the net from spraying systems, and no doubt it will be $100+. Anyone had diy experience with water injection? I wonder if an old spraygun could be modified, may require too much pressure though.

Boost Pressure Water Injection
A good quality boost-pressure controlled water injection system can be built using off-the-shelf components. The system gives an extremely fine spray and can be used with water/methanol as well as pure water. While the injection of water is not proportional to load (it is proportional to boost pressure), there is a variation in the supply of water which is still better than many systems provide. The best part of the system is that it is maintenance-free, other than requiring the refilling of the water tank as required and the occasional cleaning of the filter.

The nozzle used is an air atomising design produced by US company Spraying Systems. It has two connections - one for compressed air and the other for water. The compressed air is directed out of two orifices so that it collides with the water stream, scattering it into the tiny droplets. The pressure to supply both the water and the compressed air comes from the turbo or supercharger. The part number for the nozzle is SUE18A and it is available from agricultural irrigation and spray suppliers.

Unlike many air atomising nozzles, the SUE18A works effectively at pressures below 50kPa (7psi). Around 200 ml/min flows through the nozzle when it is supplied with water and air at around 20 psi (1.4 Bar) boost. If this flow is too great, a ball valve can be placed in the water supply hose to allow easy adjustment of the flow. If the ball valve is closed down to restrict the water supplied, the remaining water will then be even better atomised! If more than 200 ml/minute of water is required I suggest that you use two or more nozzles.

The water supply for the nozzle should be through a small water filter to avoid filter blockages occurring. An appropriate filter is available from the suppliers of the nozzle or a small garden irrigation filter can be used. The nozzle must be mounted so that it flows into the intake system before the compressor and the water should be injected after the airflow meter (if present) to prevent the water droplets upsetting the air metering.

The fluid storage container must be pressurised if the water is to be forced through the nozzle. A custom tank can be made or a large pressurised radiator header tank pressed into service. Preferably the tank should be at least 5 litres in volume for each nozzle used. Note that the tank must be capable of handling the constant cycling of internal pressures up to the peak boost level. A low fluid warning buzzer should be fitted.

Plumb the system using a ball valve to adjust the supply of water and a boost-pressure triggered solenoid (pictured) to give a positive starting and stopping behaviour. An alternative to the use of the solenoid is to install a vacuum-operated valve (such as the EGR valve) to vent the tank back to the inlet system, causing the tank pressure to more closely follow boost when the throttle is lifted. However, the solenoid valve is the safer of the two approaches: if the water ever flows into the intake when the engine is stopped, very major engine damage can be caused when it is attempted to be re-started!