Nitrous won't backfire into the engine. It will cause the engine the run lean, as the Nitrous itself isn't flamable. That may cause a backfire, but the Nitrous itself won't.

I've read the books, [Moses]so let it be written, so let it be said.[/Moses]

One molecule of Nitrogen, two molecules of Oxygen.

Mix well with gasoline (or other flamable substance) and inject in healthy doses. Reccomend Valium to get the silly grin off your face when complete.