Sunday, August 19, 2012

RSI: Water injection

Did you know that the Ford Focus WRC cars I drove had a water tank sitting behind the seat? It was filled with distilled water. Do you know what it was for? Two purposes really. A few seconds before the stage start, I switched a button on, called: STAGE. This button turned all the funky stuff on. It turned the "valves" on (diffs), the ALS on (anti lag system), the stage engine map on with max power and hence water injection. 

If you have ever heard of water injection then you will know that when the engine map is switched into stage mode, water gets sprayed in a very fine cloud, in the air/fuel mixture.


After air passes the turbocharger, it obviously gets compressed but subsequently also heated up quite a bit. 


In turbocharged engines the air and fuel mixture that enters the cylinders can sometimes explode before the spark plug ignites, usually because of extreme temperatures. It can also be due to too low octane fuels but we always used high quality fuel so bar that one. Too much ignition advance or too much turbo boost are obvious other reasons. This early detonation is called engine knock or pinging. I heard this phenomenon once in 1998 when one of the Toyota Team Sweden Celica Group A cars drove by me on the Swedish Rally. It sounds like a very high pitch rattle. This effect is extremely destructive to the engine. To avoid pinging, water is injected along with the fuel and air in the cylinders. This provides additional air cooling and therefore denser air, adding power.


The inter-cooler is there to cool the air down before it reaches the inlet manifold and if I remember correctly the injection happens directly at the entry of the inter-cooler. I may be off on this so if anyone has the knowledge please comment!

In any case water injection is a system which has been used in engines for a long time and as early as for military aircraft prior to WWII.

Back to our WRC Focus, water was also used to cool the inter-cooler radiator . There were a number of sprays which dumped water onto the outside of the radiator when the cooling fluid temperature was exceedingly high.

© 2012 Ford Motor Company


  1. Hi was water injection allowed in group A and group N??

    1. It was allowed if installed on the production car. This is why the Escort Cosworth (1992-1993) “sport” variant (without sunroof window) had a fake reservoir, pump and pipe. The system was not even connected on the road car, but it enabled Ford to use WI on the Group A. I don’t think they used it on the Group N cars.