Here's mine for XRT, which I call awesomesauce. Don't be fooled by the name. It's just a way to make you just want to download it. (I'm not a very creative person, therefore that name) I made it sound a bit like a tuned car, but I couldn't find a way to make it sound like I wanted without making it clip.
The blow off valve was taken from an actual bmw s50 turbo engine and using acid pro 6.0 I created a sound clip then loaded it into lfs to create this engine sound aswell as other sounds were made this way aswell.