For 4-turn research, science farms are really helpful, as are libraries and universities. I tend to limit my growth too much early on, but even so, I usually hit 4 turn research about halfway through the middle ages in my fast science games at emperor or below.
Libraries are helpful even when you only get one additional beaker from them, because the upkeep for the library can be paid for by income from other civs, but you can't get beakers from the money other civs pay you. This helps me justify my overbuilding of libraries.
I do tend to build at the expense of growth, so I've started playing some science games where I'm not allowed to build libraries until some specified point - not until Astronomy, or until two opponents are gone, that sort of thing. Generally I hit 4-turn research sooner this way. It just isn't as much fun for everyday, though - I like to build rather than conquer.