Firstly go to Options / Gameplay / Driving Style and select "Simulation" and set difficulty to "Expert".
Now from the main menu select Solo / Quick Game and choose the SSS from the Wales Rally GB "Chirk Castle". Then choose your preferred time of day, weather and car and crash as fast as possible into the bales as shown in the video.
I think both the engine and gearbox need to be completely red for it to be counted as "totalled".
Happy crashing !!!