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Old 13-06-2004, 10:44 AM
Richard L Richard L is offline
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Join Date: Oct 2003
Location: England
Posts: 4,936
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The quantity of water will largely depending on the following factors:

1. effective cmpressure ratio
2. fuel grade
3. egt
4. knock tendency
5. ambient temperature
6. final charge temperature
7. a/f ratio
8. how close you run your engine towards MBT timing

Most factory produced car will have all the above variables under control. As soon as you start to modify your engine - you will notice a few of the above variables will change - but if it is inside the safe-operating area of the ECU, minor adjustment to the fuel, timing etc will keep the engine safe.

Most factory fitted ECU employs the following procedure strategy to keep the engine alive with the following balancing act:

1) retard timing with mild knock (knock sensor)
2) Increase air/fuel and timimng with heavy knock.

It normally works very well until you iincease the boost pressure, the excess fuel used to cool the engine is now being uswed for power.

Under this circumstances - you must replenish the engine's cooling capability by either using bigger injectors or water injection. Since water has six times the latent heat of fuel, you need to dump six litres of fuel per litre of water!

Since un-burnt fuel has huge impact on the combustion process, it robs huge amount of power if it is used as a coolant rather than as a fuel. In comparison, the OH radicals within water enhances the burn process.
(please read turboice's WI paper)

At last you question as to how mush water to inject ? the sweeping conclusion and simplied - around 10-15% w/f ratio when you are running a few psi over the stock boost.

Quite easy to calculate: add all your injectors flowrate together and multiple it by 10% or 15% - look at the aquamist jet size/flow, that is it!





It is clear that WI injectionf
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Richard L
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