Here's the spreadsheet that shows the points workings out.
https://docs.google.com/spreadsheets/d/1wQfcX7Mj0ZPY8i2qdiwEGA7cFfnW2SakERcCnTcYyls/edit#gid=0I'll walk through the results for race 1.
For each type of car, these are the average best times:
ferrari_f40 1:48.603
ferrari_458 1:46.940
ktm_xbow_r 1:48.480
bmw_m3_e30_gra 1:50.309
The bonus points are calculated by the percentage margin from the fastest lap time, 1:46.940 for the F458. This means that whoever drove the F458 in that race gets no bonus points, because they were in the fastest car.
The other ratios to the F458 time are:
F40 = 1:48.603/1:46.940 = 1.6% points multiplier
XBow = 1:48.480/1:46.940 = 1.4% points multiplier
BMW = 1:50.309/1:46.940 = 3.2% points multiplier
So you can see what this bonus equates to in the "Bonus" column. On average, 2 points for the F40, 1 point for the XBow and 3 points for the BMW.
So for race 1, the points end up being (excuse the formatting):
1 Guybrush Threepwood ferrari_f40 102
2 Stan Daam ferrari_458 99
3 WOBBLYONE ktm_xbow_r 99
4 Steve Horvath ferrari_f40 99
5 robin ferrari_458 96
6 krahl ferrari_458 95
7 Bacchulum ktm_xbow_r 95
8 Robert Grubb ktm_xbow_r 94
9 vipergod1 ktm_xbow_r 93
10 Wally Masterson bmw_m3_e30_gra 94
11 BaFs17 bmw_m3_e30_gra 93
12 jxerri bmw_m3_e30_gra 92
13 Matthew111 bmw_m3_e30_gra 91
14 Imperious ferrari_f40 88
15 Gratulin ktm_xbow_r 87
Race 2Guybrush Threepwood ktm_xbow_r 100
Steve Horvath ferrari_458 100
WOBBLYONE ktm_xbow_r 98
Wally Masterson ktm_xbow_r 97
jxerri ferrari_458 97
Stan Daam ferrari_f40 96
Gratulin ferrari_458 95
BaFs17 ferrari_458 94
Imperious bmw_m3_e30_gra 94
Grubbet ferrari_458 92
robin ktm_xbow_r 90
krahl bmw_m3_e30_gra 91
Bacchulum ferrari_f40 89
vipergod1 bmw_m3_e30_gra 89
Matthew111 ferrari_f40 87
Perch ktm_xbow_r 85
Race 3Stan Daam ferrari_458 100
jxerri ferrari_458 99
Matthew111 ferrari_458 98
Wally Masterson ferrari_458 97
WOBBLYONE ktm_xbow_r 97
krahl ktm_xbow_r 96
BaFs17 ktm_xbow_r 95
Bacchulum ktm_xbow_r 94
Joe Stevens ferrari_458 92
vipergod1 ferrari_458 91
robin bmw_m3_e30_gra 90
Perch bmw_m3_e30_gra 89
Grubbet ferrari_f40 91
Imperious ktm_xbow_r 88
Guybrush Threepwood bmw_m3_e30_gra 86
Steve Horvath bmw_m3_e30_gra 85