There are 2 eye catching well made vintage truck mods for ETS2. The Volvo F Series by Lucasi (Top picture) and the Volvo F10-F12 updated by mjtemdark
For this sound mod some features like Turbo Lag and a little bit improved fall back of revs are added as new parameters to make the sound more realistic. If you’re the modder type and want to try such experiment you can start with switching the Asymmetric seek speed option for RPM and Turbo parameters and add values of Instant Ascending, 1000/s Descending and 0.65/s Ascending and Descending for the parameters respectively.
Anyways, Here is a preview video of the sound mod and its contents. Try to hear it with a good headphone to hear the turbo lag.