The sounds aren't great in all but a few of the cars. I did have my hopes up for the Lotus, but short of recording a clip and looping it (à la rFactor) I doubt the sounds will ever be as good as we'd all like in iRacing.
Most of the cars just sound very... tin can like, with a digital twist. There's no rumble or growl in any of the ones there should be, and I think it just comes down to the way iRacing and LFS generate sounds. They're not playing loops over and over, they're
generating sounds. I don't think the digital age has come far enough yet where sounds from a computer can bring forth such a sensory explosion as hearing any sort of race car fly by, let alone something like a Ferrari 412T or Lotus 79, in game-type software anyway.
It's funny actually, the staff guy behind the physics for the Lotus posted a quick blog about the development on the iRacing forums, people saw the video and started complaing about the sound...
The majority were quick to compliment the car and were excited none the less, but still the focus was on the sounds instead of the fact that HOLY CRAP iRacing is about to release an historic F1 car...
I shouldn't be saying any of this! Sign up for iRacing it's great, cleanest sim racing ever once you're past rookie.