Your former sentence is more accurate than your latter sentence. The key word is, "allows". Water, in and by itself is not a fuel (we know that, right?). Using water by itself adds zero power. However, as an anti-detonant, water allows the engine designer to increase power via increasing the compression ratio and/or boost pressure.

Sherwood

It allows you to run closer to Stochiometric. So, with the right fuel/air ratio, in the right amount, with water, the same ENGINE can produce more power. But it takes more fuel. And it will reduce efficiency.

Today's cars run lean, instead of rich in the "old" days.

Gee, really?

The water allows increased boost. Increased boost = more horsepower. No water= no extra boost= no boost in horsepower. Water= extra boost= extra horsepower, ergo, water injected engines are more powerful.

At any rate...it works. ;)

So do afterburners. >:}

LOL, I could be wrong. The only experience I have on the subject is I've read a whole bunch of books about it, I designed, built and installed and tuned a custom turbocharger system on a VW bug, a 2 liter 914, a 3 liter 911 (BAE kit, didn't design that one) and a supercharger on a chrysler hemi drag boat.
If we are talking about pure water injection and not water/methanol injection, it is a band-aide that covers up a tuning problem that could otherwise make even more power if it was tuned correctly.

Water cools down the combustion and slows down the combustion. It displaces fuel and air. it reduces volumetric effciency. It covers up something that is wrong. If the same engine were properly tuned for maximum power, it would work better and make more power without the water injection. In WWII it worked because they didn't have the technology or time or whatever to truly correct the problem, so they mickey-moused it with water injection.

I know people who use nitrous oxide and spray it on the OUTSIDE of an intercooler to cool it and make it more efficient. It works, but if they installed a bigger more efficient intercooler they wouldn't need the NO2.

Not to be picky, but if the engine is running close to stochiometric, the mixture is already lean. Adding more fuel takes the air/mixture away from the stochiometric range which would add more power. My contention is that merely adding water with no other changes will not add more power. Not sure if we agree or disagree.

Sherwood

Well then i guess everyone must be right.

Haha.

<---has also owned and tuned/tweaked several turbo cars.