I had 2 goes at the GR Cup yesterday too, the first race was a right mess.
1st) 6th on grid, 4th was slow to get away so i overtook into the 1st corner, i got punted off and given a 5 second penalty, then right hander after the first straight punted head on into the wall by two ahead who were fighting, i was then last and i think i finished 14th about 50 seconds behind 1st.
2nd) 7th on grid (inside for the first corner

), 3rd after the first corner, 2nd after a couple of laps, but took too much curb on the first corner on the final lap and spun, ended up 6th.
EDIT: Looks like the boost keeps refilling if you use it up after a cool down, i guess i should have used it constantly through the race. -->
https://www.youtube.com/watch?v=V349s_cRvI0