Originally Posted by mach4

Snake oil essentially. Nothing will increase mileage by 25%. To the extent it does anything it adds moisture to the intake which can reduce temps a bit and also promote cleaning the engine a bit.

Better solutions are water injection systems, some of which use a methanol mix to provide a bit more power. The technology here is sound having been used in high performance aircraft since WWII and extreme power diesels like tractor pulling machines and so forth.

Google water injection and you'll find lots of information and various systems including some nice DIY solutions.

I think there are some threads here on PP as well.