So I want to change around some engine files, ie have the lx6's sound for the xrt, fo8's for rac, something like that, etc etc. I was wondering where the default engine sounds are, i can't find them.
The samples are IN the .eng files. You can load your own sample (which isn't like a GTR sample, it's more of a gunshot sample i.e. short and sharp to simulate combusion), and then tweak how it is changed by RPM, throttle etc. Same for turbo noise iirc, and maybe some other things.
What Tristan has said is right. The only tool you need for editing .eng sounds is LFS.
Shift-a, you can load and save samples, and tweak the way the engine modifies the sound. That's the ONLY way to modify the sounds.