So did you already find how to modify speed of vehicle sounds?
speed of sound? i think you got it wrong, i said "make to change the speed and sound of engine"
And about objects - you can attach them to car in way like extras are attached - create a copy of needed model as atomic and add it to vehicle clump. For me it is the best solution here,
interesting, tell more about this
i'm creating the "BMS Sound Shop" all with objects attachs, and some objects "moving-attaching"