Like the big rigs (Class8) all diesel trucks have an inherent lack of stopping power add 10,000lbs or more on a down grade and the truck will want to start to runaway, causing you to ride your service brakes. Riding your service brakes causes heat, brake fade and premature wear.
With the big rigs they use what is called an engine brake, these brakes work by opening the exhaust valve on the compression stroke, forcing the gases out of the exhaust thus causing the piston to return to the bottom of its stroke under its own lag. It is these gases being pushed out the exhaust that causes the burping noise you all hear as the truck is going down hill.
With the smaller displacement diesel engines (as in the Ford Powerstroke, Chevy/GMC Duramax, and Dodge Cummins Ram) an engine retarded or engine brake is not available due to the amount of compression and space developed.
This is where an exhaust brake
comes in, used widely in the medium duty truck market (5 tons) Class A Motorhome’s tow trucks and such exhaust brakes are also available for the personally use vehicles.
Unlike an engine brake an exhaust brake
works by closing the exhaust gases off that are trying to escape the engine. This is done by placing a butterfly valve in the flow of the exhaust; once the brake is activated the butterfly closes to restrict the flow of exhaust. By restricting the flow of the exhaust no noise produced like and engine brake in the larger trucks. When you step on the throttle the exhaust brake
shuts off and the engine returns to normal.
Each engine manufacture has its own set of backpressure specifications that exhaust brake
manufactures must adhere too to ensure no engine damage can or will occur. The maximum back pressure limit is set by ether placing a hole in the butterfly or only partially closing the butterfly off at the engines maximum RPM.
Now with this being said all exhaust brakes are created equal at the maximum engine RPM’s. Unfortunately, with these types of designs, as the engines RPM’s decreases below1900rpms the Backpressure (holding power) fades away as the hole in the butterfly or partially closed butterfly do not change to compensate for the lose of retarding performance.
What sets some exhaust brakes apart from others is the ability to regulate the engines back pressure throughout the entire RPM Range. By regulating the back pressure the result is a longer duration of braking thus saving your service and trailer brakes from heat that can cause brake fade and premature wear. Add this to a vehicle with or without the tow haul mode and towing anything above 10,000lbs becomes a dream. The exhaust brake
can be used even when not towing thus saving your brakes during every day driving.