I'm still testing, but I like it. It's much better than your first attempt, and I think it's better than the current Trigger engine sound: yours is clearer, and better conveys the roar of a racing car. One remark is that it seems (to my ears at least) that it has some undertones of an electric car. What do you think?

I think it sounds 'weaker', 'less powerful' and 'higher pitched'. Let me know if you think one of these [1] [2] is good enough for being committed :) :

[1] http://omploader.org/vY3Zsdg
[2] http://omploader.org/vY3ZsdQ

Here is how I created them:

sox ~/engine-loop/engine-loop-1-normalized.wav sounds/engine1.wav pitch -60
sox ~/engine-loop/engine-loop-1-normalized.wav sounds/engine1.wav pitch -200
engine-loop-1-normalized.wav [3] from:

[3] http://opengameart.org/content/car-engine-loop-96khz-4s

I have another question regarding the (background?) sound that the engine makes when in neutral gear. It always sounds strange to me (all 3 versions) and I can't understand what it's supposed to represent. If it is the sound of an engine in idle position, does it manage to convey that?

I don't know what exactly the sound engine of Trigger does, but I assume it's either a pitch or playback speed shift, depending on car engine speed. Trying out alternative functions for defining that effect might be interesting for a programmer on the team. :)

The car engine standby sound is simply the lower boundary of the effect used.
PS While we're at it, do you think we can do something about the 'slide' sound, and the 'impact' sound? Both always felt a bit brutal to my ears.

Yes, we have to at some point, for licensing reasons :) If they are just too brutal=loud, volume might even be changeable via code.

I admit that I quite like the current slide/gravel sound.