The sim uses only UDP traffic, so if the others using your Internet connection are using mostly TCP, and you can give priority to UDP traffic, that would be an easy first step.
There are two ends to each communication: the local end (your computer), and the server end (our server).
For the sim:
We use "ephemeral" ports on the local end. This means that your computer finds an unused port number, and uses it for its end of the connection. There is not much you will be able to do with that, since most programs do this same thing.
We use a fixed range of ports (15000..52500) on our race servers. Hopefully, you can specify port ranges, and not just individual port numbers.
If you can give priority to (remote) IP address ranges, instead of port numbers, that may be more reliable.
Note: Servers listed below do not necessarily mean they are running as they are taken in and out of maintenance.
US East
bosrace01-orig.iracing.com --> 67.218.1.1 --> 2620:13d:e000:100::1
bosrace02-orig.iracing.com --> 67.218.1.2 --> 2620:13d:e000:100::2
bosrace03-orig.iracing.com --> 67.218.1.3 --> 2620:13d:e000:100::3
bosrace04-orig.iracing.com --> 67.218.1.4 --> 2620:13d:e000:100::4
bosrace05-orig.iracing.com --> 67.218.1.5 --> 2620:13d:e000:100::5
bosrace06-orig.iracing.com --> 67.218.1.6 --> 2620:13d:e000:100::6
bosrace07-orig.iracing.com --> 67.218.1.7 --> 2620:13d:e000:100::7
bosrace08-orig.iracing.com --> 67.218.1.8 --> 2620:13d:e000:100::8
bosrace09-orig.iracing.com --> 67.218.1.9 --> 2620:13d:e000:100::9
bosrace10-orig.iracing.com --> 67.218.1.10 --> 2620:13d:e000:100::10
bosrace11-orig.iracing.com --> 67.218.1.11 --> 2620:13d:e000:100::11
bosrace12-orig.iracing.com --> 67.218.1.12 --> 2620:13d:e000:100::12
bosrace13-orig.iracing.com --> 67.218.1.13 --> 2620:13d:e000:100::13
bosrace14-orig.iracing.com --> 67.218.1.14 --> 2620:13d:e000:100::14
bosrace15-orig.iracing.com --> 67.218.1.15 --> 2620:13d:e000:100::15
bosrace16-orig.iracing.com --> 67.218.1.16 --> 2620:13d:e000:100::16
bosrace17-orig.iracing.com --> 67.218.1.17 --> 2620:13d:e000:100::17
bosrace18-orig.iracing.com --> 67.218.1.18 --> 2620:13d:e000:100::18
bosrace19-orig.iracing.com --> 67.218.1.19 --> 2620:13d:e000:100::19
bosrace20-orig.iracing.com --> 67.218.1.20 --> 2620:13d:e000:100::20
bosrace21-orig.iracing.com --> 67.218.1.21 --> 2620:13d:e000:100::21
bosrace22-orig.iracing.com --> 67.218.1.22 --> 2620:13d:e000:100::22
bosrace23-orig.iracing.com --> 67.218.1.23 --> 2620:13d:e000:100::23
bosrace24-orig.iracing.com --> 67.218.1.24 --> 2620:13d:e000:100::24
US West
Dynamically allocated IPs
usw1race01-orig.iracing.com
usw1race02-orig.iracing.com
Australia
Dynamically allocated IPs
apse2race01-orig.iracing.com
apse2race02-orig.iracing.com
apse2race03-orig.iracing.com
apse2race04-orig.iracing.com
Germany
Dynamically allocated IPs
euc1race01-orig.iracing.com
euc1race02-orig.iracing.com
euc1race03-orig.iracing.com
euc1race04-orig.iracing.com
euc1race05-orig.iracing.com
euc1race06-orig.iracing.com
euc1race07-orig.iracing.com
euc1race08-orig.iracing.com
euc1race09-orig.iracing.com
Japan
Dynamically allocated IPs
apne1race01-orig.iracing.com
Brazil
Dynamically allocated IPs
sae1race01-orig.iracing.com