i think what im hearing that is distracting with the sounds is the atmospherics. if i was tackling this sound modding id be trying to differentiate those 2 key elements, engine in atmosphere, engine not in atmosphere. i feel by adding these freely available sounds your adding atmopshere in places you really dont want it. its also like a photograph, we cant add them because theres no real reality for it to work in. If you look at what 1c have done already its basic for sure. but the principle of the layering with the sounds gives the CEM its premise involvment. i would attack this by layering multiple sounds to get to where you want. not necissarily starting with a new sound.

a hard one but im sure you guys will master it.