Dark-matter afterburner

The Dark Matter Afterburner is a creation by Professor Farnsworth to for the Planet Express Ship to deliver 200% fuel efficiency. The idea for it came to him in a dream but forgot about it in another dream. He showed that invention to Cubert, who think that it is "impossible". As of Bender's Game these have been converted to use whale oil.

Trivia

 * Getting the idea for an invention in a dream is a reference to the  movies.