The cheapest way would be the basic Aquamist system, BUT you would need to use this in conjunction with one of our ACT gauges (with the WI facility). This is because the Aquamist set up is flawed in that it only works off boost pressure. However, you want it to work of boost AND ACT. i.e. the water is ONLY injected into the engine if the boost is above (user set psi) AND the ACT is a above (user set temp). If you inject water into the system on a pressure only basis and the charge temp is not sufficient to absorb the water in the heat exchange process, it will lead to mis-fires and poor running.