Unsolved multiple engines with different sounds

You're problem might be the same I have been struggling with for an entire Saturday.
when you do step 5, adding: "engine": { "soundGroup": "soundgroupname" }.
make sure it's not added under torque, friction, burnefficiency etc. in the mainEngine section, but simply under engine: between props and nodes. Check the screenshot! I wasted an entire saturday until I figured out the correct syntax.

all the below is for the benefit of other people checking the thread.

1) create a "sounds" folder in your vehicles folder
2) move here your oggs you want to use
3) write an sbeam file like this:

{
"modifiers":[
["name", "source", "factor", "offset", "min", "max"],
["engine_throttle", "throttle", 1, 0, 0.65, 1],

],
"sounds":[
["group", "filename", "profile", "nodeName", "source", "factor", "offset", "minVolume", "minPitch", "maxVolume", "maxPitch", "pitchBlendInStartValue", "pitchBlendInEndValue", "volumeBlendInStartValue", "volumeBlendInEndValue", "volumeBlendOutStartValue", "volumeBlendOutEndValue", "volumeModifiers", "pitchModifiers"],
[ --soundGroupname-- , --ogg idle-- , "AudioDefaultLoop3D", "ENGINE", "rpm", 1, 0, 0, 0, 0.8, 21.12, 0, 20000, 00, 200, 2000, 3000, ["engine_throttle"], [] ],
[ --soundGroupname-- , --ogg low-- , "AudioDefaultLoop3D", "ENGINE", "rpm", 1, 0, 0, 0, 0.8, 21.12, 0, 20000, 0000, 200, 2000, 3000, ["engine_throttle"], [] ],
[ --soundGroupname-- , --ogg mid-- , "AudioDefaultLoop3D", "ENGINE", "rpm", 1, 0, 0, 0, 0.8, 21.12, 0, 20000, 0000, 200, 2000, 3000, ["engine_throttle"], [] ],
[ --soundGroupname-- , --ogg high-- , "AudioDefaultLoop3D", "ENGINE", "rpm", 1, 0, 0, 0, 0.8, 21.12, 0, 20000, 0000, 200, 2000, 3000, ["engine_throttle"], [] ],
[ --soundGroupname-- , --ogg limiter-- , "AudioDefaultLoop3D", "ENGINE", "rpm", 1, 0, 0, 0, 0.8, 21.12, 0, 20000, 0000, 200, 2000, 3000, ["engine_throttle"], [] ],

4) the numbers in the red rectangle on the screenshot are in order
--the rpm to start blending in the sound
--the rpm to finish blending in the sound
--the rpm to start blending out the sound
--the rpm to finish blending out the sound
so it slowly becomes full volume and then fades out across the rev range. You specify where exactly.

5) now you go to the engine.jbeam file

and you reference the soundGroup that you've made in your sbeam file.

If you want to understand sbeams and attributes in the file a little bit better, this is a good thread to read:
https://www.beamng.com/threads/help-deciphering-sbeam-file.28119/

For an alternative method, here's this, although it needs a single ogg sound:
https://www.beamng.com/threads/can-an-sbeam-be-gear-based.36153/

There was a third important thread on what the different attributes do in the sbeam file but of course I can't find it just now. Anyways, good luck