My favourite ramen in Sydney is Gumshara. It's a small place in a food court near China Town. The setting isn't great, it's not the most amazing atmosphere but it's all about the ramen.
I highly recommend the pork rib ramen, it's my go to bowl. All the soups are very filling. The pork broth is nice and thick but can be adjusted to taste.
Gumshara is in the Eating World Food Court. Dixon Street, China Town Sydney
Happy slurping.