You can increase the range of a CB by installing a 107" steel whip or a fiber glass whip with a ball mount that you can get at a good price at a big truck stop.
American CB radios are not legal in Australia. Due to specs.
In Australia they need a license to operate in the 11 meter CB band.
In USA there is no license requirement.
A good CB installation will be achived with a long antenna, a good ground system, grounding the antenna base and CB radio to the vehicle chassis will improve reception and transmission. If you experiencing ingnition noise in the RX/TX change the spark plugs and spark plug wires or reposition the CB radio/antenna will help most of the times or you can get a filter that oues on the red/black power wires directly from the battery.
For greater range get a CB radio with AM/SSB, SSB (single side band) has an output of rf signal of 12W max and AM only 5W.
If any1 wants more information I will help you, I am a license amateur radio operator since 1991. Good luck and have fun.