[H] When and How Transition to Raven/BC in TvZ

  (Edited: )

Hi, I am a high diamond(number 2 in division, playing masters regularly), and I am struggling with late game TvZ. I usually open up with a 1 rax FE into huge a 2/2 biomine push after applying pressure some after 1/1 finishes. My build is pretty refined up to the push(although my macro slips a little during the battles), but once I start getting to the the point where the Zerg has ultralisks, I feel like I cannot engage his army, and I can't drop because most zergies will spore and spine a ton at each base and keeps 8 marines from doing a whole lot. Once he gets corruptor brood lord, I usually just lose because I can't deal with the BLs and ultras together. I  always want to go into raven BC late game, but I can never find a good time to be able to add on more starports and stop producing marine marauder. I also have trouble finding a good thing to do with the bio army except to just trade armies, and the trades usually aren't worth it.

when should I start transitioning into raven BC, and how should I go about it? I will post some replays soon, I'm on my phone ATM :D

Here is a replay of how the games usually play out http://drop.sc/334794