[Richard L]

I would not expect a great deal of economy gain by adding a water injection system especially for a non-turbo engine. Th eonly way you can get better mileage from the same engine is by increasing the static compression ratio and use water injection to suppress knock.

But, if you are suffering from bad fuel of high ambients, there will be some small benefit. Water inejction can then be used to recover the powwe loss.

Richard