I think it's fair to say that inside a car, when you're driving at full throttle, it's bloody difficult to hear anything else. You could argue that a road car isn't that loud, but - hang on a minute - it's also full of sound deadening. As a general rule, the louder a car is, the less soundproofing it's going to have, right? So, as the soundproofing level allows more noises in, the engine drowns more out when you're at full tilt.
Driving a Lotus Exige - yeah, I know having the engine right behind your head and barely soundproofed at all doesn't make this the best example in the world - on track, and passing within five yards of another Exige at 8,000rpm and full throttle, I couldn't hear the other car at all. All I could hear was wind, tyres and engine from my own car.
To turn it to LFS, I was sitting at the side of the track, in car with engine running, at Aston - and I heard an AI BF1 moving on a part of the track that was some considerable distance away, not approaching me or anything - just on a part of track that happened to be near to mine, and I could hear it. It's not that bad. However, yes, you can hear cars like that from a serious distance: camping roughly half a mile from the nearest point of the circuit at Le Mans last year, I could pick out and identify individual cars testing on track. You can hear them from a very long way away.
It's not just race cars either - I live fairly near a fast bypass that's not used often, so in the middle of the night it's not at all uncommon for me to lying in bed and listening to someone with a V12 opening the pipes on a road that's over a mile away. And I can still hear them, clearly enough to count the gears, when they're at least two or even three miles from where I am. In a house.
Standing trackside at something like the MotoGP, the bikes are so massively loud you can feel your drink vibrating, and the same goes for LM GT1-class and LM P1-class petrol cars. Back to LFS, if you just sit at the pit wall in shift-U mode, you can't hear things anywhere near as much as you would in real life - but this could be entirely deliberate. It would be pretty annoying after a while if you could hear every car all the time, not to mention the extra processing power used in making the sounds.
Sam