This mod is Cummins ISM with straight piped sound for SCS and modded trucks

Version 2.0 Changelog:
-Total mod rebuilt
-Yeah that one changelog totally does the job.

Version 1.0 Feature:
-Cummins ISM 280-500HP with straight piped sound
-Custom sound attenuation for realistic sound fade off with distortion effects
-Custom exhaust distortion for realistic exhaust tone and works along with custom attenuation
-Custom sound orientation for realistic sounds from different angles
-Realistic turbo behavior
-Included idle jake brake system
-Included Improved Customizable Additional Supported Trucks (CAST) in the mod
If you don't know what CAST is :
https://steamcommunity.com/workshop/filedetails/discussion/665335536/3156453942274154402/

Quick tutorial on how to use CAST
1. Goto def/vehicle/truck/
2. Rename one of zcustom_xx into truck def name you want
and you should good to go

How to use idle jake brake:
1. hold light horn button (J button) for 1 second, then release
2. tap light horn button once again, and idle jake brake should be engaged
3. Repeat the same process to turn off 

Note: idle jake brake system will not work with some kind of interior sound mods

Credits:
Slav Jerry - sound samples, mixing and modding