There is actually not much difference between Champ Car and IndyCar, except that the chances are you have heard of IndyCar, since you have seen or heard of the Indianapolis 500 race. The Indy 500 is the major event of the IndyCar season, and you might think that the cars look like F1 cars. Again, however, this is only an illusion, as an IndyCar again, is nowhere near the technical level of an F1 car.
Be warned, however, that IndyCars probably go at a higher top speed than an F1 car during the Indy 500. So F1 racing is NOT about being the fastest cars in the world in finite terms. They ARE the fastest cars in the world on their own tracks, though, and they might possibly be - with some alteration - faster than IndyCars on an IndyCar oval track.