Back to the Speedbowl and it's not that hard.
Vehicle : CYGON Tempest (level 19 unlock)
Speed Demon
Liddo 5 / Speedbowl / Rating : Easy
Number of laps : 5
Number of Combatants : 2
Puckups and Catchup on
Destructible off
Engine Power : WILD
For the first lap Just do it normal on the main ring, getting 3 turbos and hitting all the boost pads. One powered up and one regular. On lap 2 ride around and hit the boost pad in the center of turns 1 and 2. As soon as you hit it use your regular turbo. Once you get on the backstretch hit all of the boost pads, use your button boost and the powered up turbo. Make sure to pick up more turbo before going around turn 3. Hit the boost pad inbetween 3 and 4, grabbing turbo at the exit of turn 4 and charge that up. Repeat 3 more times to get over 700 kph. I messed up on lap 5 falling to the bottom ring in the back stretch but still got an average speed of over 715. You'll be getting Mach 1 a bunch of times this race as well if you do it correctly.
Here's a video of me doing it and the fastest I've gone.
https://1drv.ms/v/s!AsUOa7YS1T9Ps80zaJQoWKPAsQ-X-w