I think we should start our discussion about sound in LFS from the question
"What engine elements are making THE BASIC engine sound in LFS".
Is it only a sound of cylinder stroke, or maybe the valves and cams are making the noise?
Is this stroke sound always the same, or maybe it changes during load changes?
Maybe there should be few different strokes to play, ordered by the engine load.
Next thing to mention is stroke timing.
As you know we can have earlier/late stoke, which also should be considerated.
Next we can think about slight variations in the low revs. Which will add more reality.
But we are coming more and more into combustion cycle simulation. Maybe it is the key point?
We all know that the LFS engine sound is not good when going up the revs.
What causes the sound to be wilder in RL? Is it only louder detonation,
or maybe valves and cams are working faster and faster producing a lot of additional noise.
From it there is only one step to Honda VTEC technology simulation.
Maybe the lack of simulation in one of the above elements
is the point of unnatural sound representation.
BTW.
The engine load transferred by the clutch is not properly simulated.
Maybe it is causing by the bugs in clutch simulation, but for me load changes during changing gears are too rapid.
When clutch is re-engaged, engine revs are quickly changed, without transition.
There is no clutch slip, or the slip is too low. In my car when I drop clutch,
the revs are not simply switching into different value, but they are noticeably increasing.