Hi, you should post this as a forum instead of the model database. That way it's easier for people to comment and well, that's what it's made for. The model database is mostly just for finished rides. Anyway, I saw the video (on your channel, it isn't working for me here) I posted a comment there. Basically all I said was that you should make the dive loop a little taller and add an extra support. 

^ Yeah for future notice put this in the construction thread, but I didn't really understand where to put things when I joined either There are a few ways you can conserve some speed: Stronger supports, more connections to the track with each support, smoother track with less jolts. I saw in the video the base shook quite a lot when it went over the dive loop, so if you can keep that rigid you'll save more speed. I don't know how it works with the slim cars, but you could try weighting them and using silcone spray on the axles of the wheels to reduce friction and perhaps using a longer train too. On another note the drop becomes too steep too quickly, so you might want to change that. 

This is a very ambitious project though, so good luck, I hope it works out for you and that my comment was not completely useless. However, if I were you I might try some smaller projects first to perfect your shaping and speed conservation before massive projects like these. 

^In addition to what he said, stagger the rods of your spine so a new one will always start around the halfway point of the rod on the other side. The way you have it set up now causes the track to be sharp where the rods end, though I see what you were trying to do with the red rods. This will smooth the track out quite a lot which will help speed, and it will look better.

Just a note, to get your video to work, you just want to copy the very last part of the URL, not the whole thing. I fixed it for you in this case.