I use faith to cement space race victories. I do this by getting rationalism and order so that I can buy both Great Engineers and Great Scientists. The Great Scientists discover technologies that allow the Great Engineers to be able to rush the science oriented wonders that come with them.
If you don't have your own religion you can't purchase them with faith. I don't know if you can purchase GP either?
You can't purchase them unless the religion in your cities is your own? I've not had a game where I didn't found my own religion, so I didn't know this. I had sort of taken it for granted that you could always make those two units as long as you had any religion at all in the city (with the missionary spreading that religion rather than your own).