First thing to note, they are being extremely cautious about letting anyone hear the new cars running, even Alpha Tauri who always put sound clips up have stayed quiet on the AT02 running. This has to be a hype thing and the engine maybe sounds drastically different? Surely not a competitive thing hiding from the competition at this stage of the game? I'm just surprised there is no soundbites whatsoever...
Just came across this video on twitter that was posted a couple hours ago after they finished RB16B filming day.
1:12 into this video, not sure if intentionally subtle.. but whatever engine that is accelerating, it's not the Honda we are used to! RA621 tease?