You guys aren't taking into account the fact that Hydrogen and Oxygen are both more volatile fuels than gasoline. Meaning you will get MORE energy from burning those two than you would get from burning the same amount of gasoline.
Oxygen is not a fuel, it is an oxidizer http://en.wikipedia.org/wiki/Oxidizer
The other thing you are not taking into account is the density of hydrogen. Since these "systems" being discussed in this thread are not compressing hydrogen at all there is only a minuscule/negligible amount of the gas entering the system. Barely more than is avaialbe in the ambient air.
To put it another way, in order to get hydrogen to the same energy density as gasoline you have to compress it: A gallon of gasoline is around 6 pounds, and has 126,000 Btus of energy in it. A gallon of hydrogen (gas) only contains around 40 Btus in it. Quite a difference! Instead of a two cubic foot gasoline tank (15 gallons) in your car, you would need a tank more than 3,000 times bigger, over 6,000 cubic feet, for the equivalent Hydrogen! That's a little more than TWO standard semi trailers (8'wide x 8'high x 45' long or 2900 cubic feet each). Pretty big gas tank!
Well, that is obviously not going to happen! So, the many ongoing explorations into using Hydrogen as a fuel always involve carrying HIGHLY COMPRESSED Hydrogen in very thick, heavy tanks. If you have ever seen the kinds of tanks used for the Oxygen for a worker's oxyacetylene cutting torch, that's the kind. Such tanks can hold Hydrogen at around 100 times atmospheric pressure, or 1500 PSI, an extremely high pressure (or even higher) (We will later mention even higher pressure hydrogen tanks at 3000 PSI).
Well, at 100 times atmospheric pressure, the Ideal Gas Law tells us that the Hydrogen would now only take up 2900/100 or 29 cubic feet. That works out to around 60 of those (fairly large) high pressure storage tanks (to match the effective capacity of the 15 gallon gasoline tank.). Each tank is very massive to withstand the very high pressure, and each weighs nearly 100 pounds empty. (And around 1/4 pound more when filled with Hydrogen!) So the normal American car which presently weighs around 2800 pounds would have around an extra 6,000 pounds added, so the vehicle would now weigh more than three times as much as current cars! (This tremendously affects acceleration, handling and other performance, and it would be like that car pulling a huge 6,000 pound trailer behind it.
Source: http://mb-soft.com/public2/hydrogen.html