Exhaust brake for gasoline engines

In summary: When you let off the throttle, the vacuum created by the cut in the air flow allows the piston to drop back down to the bottom of the compression stroke, which then delivers power back to the engine.The main drawback of using engine braking in this way is the limited supply of engine power. In addition, the engine braking system can also create drag and decrease fuel efficiency.
  • #1
Everything I've read about them has said they would be ineffective or have very minimal benefit due to lower compression on non-diesel engines and other factors. Yet I am aware of one that sold well in the '80's and '90's and was tremendously effective as a "mountain tamer" in the RV industry with no notable drawbacks. There's much more to the story, and this being my first post, I'd rather keep it brief and have a discussion as to the viability of a gasoline engine exhaust brake system. Thank you.
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  • #2
First we need to note the difference between an exhaust brake (where the exhaust is simply obstructed) and a Jake Brake (where the engine is used to compress air).

Even if you don't have an exhaust brake, keeping your engine in gear while descending a steep hill will spare your brakes.
Mt Washington (6289 feet) is a few hours drive from where I live. I have seen the results of drivers trying to descend that road without using low gear and without stopping to rest their brakes. The result is a lot of heat, a lot of smoke, and a car that will cannot fully come to a stop without hitting something.

So given that a non-diesel engine is already capable of providing some braking. Any incremental improvement will be that much more beneficial.

The key advantage in engine braking (low gear, exhaust braking, or Jake braking) is that the engine is bigger that the brake with a more effective cooling system. So it is in a better adapted to slowing the vehicle without damage to itself. This braking isn't a replacement to use of the braking system - but is supplemental. It takes enough of the load away from the brakes to keep the brakes from overheating in heavy (but not urgent) braking situations.
  • #3
https://en.m.wikipedia.org/wiki/Compression_release_engine_brake said:
The name is derived from the manufacturer, Jacobs (of drill chuck fame), and was patented 1962–1965 by Clessie Cummins.[1] When the driver releases the accelerator on a moving vehicle powered by an internal combustion engine, the vehicle's forward momentum continues to turn the engine's crankshaft. With Mercedes diesel engines being a notable exception, diesels by design have no throttle butterfly in the intake so regardless of throttle setting a full charge of air is always drawn into the cylinder. As such, even with fuel supply cut off and thus new detonation prevented, each time air is compressed in a cylinder virtually 100% of that passively generated energy is returned to the crankshaft, providing very little in the way of engine braking to the vehicle.

The typical compression release engine brake, as originally developed, uses an add-on hydraulic system using engine oil. When activated, the motion of the fuel injector rocker arm is transferred to the engine exhaust valve(s). This occurs very near the engine's "top dead center" (or TDC) and releases the compressed air in the cylinder so that the energy is not returned to the crankshaft. Energy is instead expelled out the exhaust system rather than being retained in the drivetrain. If used properly, a compression release brake can assist a vehicle to maintain speed or even slow it with little or no use of the service brakes. The power of this type can be around the same as the engine power.[2]

Contrast a petrol engine under deceleration, where a closed throttle prevents free flow of air into the cylinders, resulting in little pressure to release at the top of the compression stroke. The closed throttle provides engine braking by forcing the engine to generate a vacuum between the throttle and the cylinders.

The key difference is that when you cut the throttle in a gas engine, you cut both fuel and air flows, but in a diesel you cut only fuel.

1. What is an exhaust brake for gasoline engines?

An exhaust brake is a device that is installed on gasoline engines to help control the speed of the engine by utilizing the exhaust system. It works by creating backpressure in the exhaust system, which helps slow down the engine and reduce wear on the brakes.

2. How does an exhaust brake for gasoline engines work?

The exhaust brake is typically controlled by a valve that is installed in the exhaust system. When activated, the valve closes and creates backpressure in the exhaust, which helps slow down the engine. This backpressure is created by restricting the flow of exhaust gases, which reduces the amount of air and fuel that can enter the engine, ultimately slowing it down.

3. What are the benefits of using an exhaust brake for gasoline engines?

An exhaust brake can help improve the overall performance and efficiency of a gasoline engine. It can also reduce wear and tear on the brakes, as the engine is helping to slow down the vehicle. Additionally, using an exhaust brake can help reduce the risk of overheating the brakes, especially when towing heavy loads.

4. Are there any downsides to using an exhaust brake for gasoline engines?

One potential downside of using an exhaust brake is that it can increase the amount of exhaust backpressure, which can lead to decreased fuel efficiency. It may also cause increased wear on the engine if it is used frequently or for extended periods of time.

5. Can any gasoline engine use an exhaust brake?

Not all gasoline engines are compatible with an exhaust brake. The engine must have a turbocharger or supercharger and an exhaust system that can accommodate the installation of the valve. It is important to consult with a professional mechanic before installing an exhaust brake on a gasoline engine to ensure compatibility and proper installation.

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