So Torro Rosso is just like a few others in that they have started to drop some info such as this...
https://www.youtube.com/watch?v=ZKI32W4yJTQ
A few points. Note, they say RA618H. This is the designation for the 2018 Honda engine and not the 2017 engine. Between TR saying they have mated and test fired the 2018 engine with the 2018 chassis and reports elsewhere that testing by Honda on the 2018 engine are going well, I think this mostly puts to bed the potential for TR starting the season with the 2017 engine.
Of course, lets see how things go in pre-season testing!
Given each driver is limited to three ICE per season now,
there will be limited opportunities to introduce significant improvements during the season. I am reading elsewhere that they have a planned mid-season upgrade that is expected to be a significant change, but also something they are testing right now. So it sounds like the early 2018 spec is mostly set and they are working on a mid season spec. Also it looks like the launch spec is not identical to, but based upon the unraced "spec 4" concept from last season (no reason to ignore other improvements that may not have been in last years spec 4).
Saying this sounds like this is another full re-engineering of the engine. No, this all is supposed to be evolutions of the base 2017 design. I expect much work was focused on combustion as well as MGU-H (particularly reliability).
Oh! And the photos are of the 2017 engine. They are not showing the 2018 engine on purpose (as many details can be gleaned from just the exterior).
Honda did however release some interesting info in the Japanese press around the 2017 engine awhile back. They are probably more open than any other manufacture at the moment.
Richard