just messed around with it .. i made this distorted (way 2 loud) Civic Turbo Vtec engine sound
on the XRT car.. its pretty funny..
made a different supra kind of dumpvalve in it and a vacuum-sounding turbo
imho there should be an ability to load a wav file on the engine itself (L button).
anyway unpack the file to engine folder.. type /edit_eng then shift+a and load the ENG file for XRT car. to try it out.