This mod is CAT 3406E 2WS engine straight pipe for some SCS trucks and many modded trucks.

Latest Version Feature:
-CAT 3406E 2WS 435-550HP and 700HP Tuned engines with straight pipe sound
-Automatically activated engine fan
-Exhaust stack simulation effects
-Sound attenuation effects for realistic sound fade off from the distance
-Sound distortions and directional effects for realistic distortions from different positions around the truck

Credits:
Slav Jerry - sound sampling, mixing, mastering