From the public Early Access build: https://store.steampowered.com/app/21...
This strat was inspired by this video from Super Bnns that showed a way to go over 10,000km/h on Funnel Dive:    • Ivory Mako on Wavia - Aero GPX  
EDIT: D1rty Dan came up with an earlier lap 1 "hamster wheel" strat:    • Aero GPX Time Trial: Wavia - Funnel D...  

When going for this "360 no scope" strat, it's vital to exit the tunnel at an angle that gives the machine very little height; it's super easy to fly too high over the finish line at these ridiculous speeds, and doing so will skip a checkpoint and the lap won't count. I've tried a few different setups to get a low exit but the one I went for in this run is to drive on the middle line of the tunnel while going roughly 3000km/h give-or-take a few hundred km/h, then just start and fully hold a Hyper Slide to the left at the right time to hit all 3 boost rings without accidentally flying out of the tunnel before completing the 360. Whether or not you get a low exit depends a lot on minor variations in speed, angle of approach before the Hyper Slide, and the timing of the start of the Hyper Slide.
I seriously doubt this is the best setup for the 360 (especially when starting at 3500km/h+) so if you're going to try this yourself, I encourage you to experiment with different lines in practice mode.

The spin attack animation was disabled via the settings menu to make it easier to perform better spin grinds.

0:00 - The run
1:28 - Extremely low tunnel exit
1:33 - Rare lap 1 boost refill, but mistimed the 360 at the end of lap 2
1:57 - 6000km/h+ lap 2 entry, but jumped over the lap 3 trigger