You need to put the files to directory: /data/engine.
If you want to edit things yourself, start LFS and get into the car you want to modify. Press T and type "/edit_eng" and then press shift+A. You should get the sound editing panel visible. On the right hand side you see "L" buttons. Click the L next to dump valve and select a sound. Sounds must be in /data/engine directory, i think.
For me, it was a hard decision... Do I want the dump valve sound, of turbo stalling sound.
Well, "both is better", I thought. It actually sounds like a too small dump valve. :crown:
Try the attachment, if you want. Also the .eng file is attached, I tweaked the engine sound a little too. Make backup for your original XRT_default.eng file and extract the files to /data/engine.