Make a wave player, make an input value (float) called RPM. Connect that to the pitch of the wave player. Make a BP that tracks the RPM value of the vehicle and send that parameter to the RPM value of the metasound (as you would with a sound cue). Now you should have pitch modulation at least.
Volume automation or crossfade, you could get by taking the RPM float value and make a mixer that crossfades according to the same float.
Here you go 
