Regarding exhaust brakes:
Gas engines have a throttle so provide a certain amount of restriction natively. This acts somewhat like a brake.
Diesels without exhaust brakes have little natural compression braking since they only have the friction of the spinning engine and no restriction in the airflow to slow them down.
Now with exhaust-restricting turbos you can add significant resistance to the coasting engine.
Here is the big difference between restricting the intake (gas engine throttle) and restricting the exhaust (diesel exhaust brake): With an intake restriction you can only pull down to as low as a perfect vacuum which is less than 15psi. On the exhaust side you can build much higher pressure than that which provides a much stronger braking effect because it takes more energy to build higher pressures.
