Hi guys. I'm the original creator of the fluttery turbo sound. It was taken from a video on youtube of a Holden VL Commodore Turbo with a "dose" pipe as they call it. This is a setup with no blow off valve installed. The sound you hear is air being pushed back through the turbo and the blades on the compressor wheel chopping up the air.
The sound was recorded and modified in such a way that it could be effectively looped by the LFS sound engine.
Here is the link to the sound on my webspace.
http://crashdummy.ugbox.net/files/lfsflutter.rar
The archive retains the directory structure so you can just unrar it directly to your LFS directory and the files should be put where they are needed.
Once you've done that just get into the car in game and press Shift +A and load the profiles.
That's all there is to it