When I say engine braking, I mean real engine braking, not a Jacobs brake, I’ll get to the difference in a second. No, I mean using the forces at work inside an unpowered gasoline engine to decelerate said gasoline engine without any external assistance. Why do I say it’s better? Because you’re not grinding down your brake pads to help you stop.
Definition of Engine Braking
The most common thing to be called “engine braking” is a compression-release brake, “Jacobs brake”, or “Jake brake”, is not only just applicable to diesels for the most part, but also something that is, in many cases, illegal.
I’m referring to literally just letting off the gas. See, in a modern car, when you let off the accelerator pedal, the computer does two things:
- Shuts off the fuel injectors (this is why your MPG reads 99.9)
- Completely closes the throttle value, meaning it heavily restricts airflow to the engine.
The combination of these factors is that the engine is now unpowered, that is, with no gas in it, it is no longer producing force, and that it’s now under a vacuum. Because it’s become a load, not a generator, all movement is going to slow to friction, this is why you start to slow down slowly when you let off the pedal and coast. At high(er) RPM, the vacuum the engine is fighting against adds extra load, causing it to slow down faster. The faster the engine spins, the faster it wants to stop spinning.
When you downshift to a lower gear, this causes (simplified) the engine to speed up. As we mentioned, that causes it to want to slow more. This also, well, revs the engine, leading me to explain to more than one passenger why I’m revving it while going to a red light… I’m not.
Even the Wikipedia article cites engine braking as being useful going down hill, because the retarding force of the engine slows the car without needing to use the foot brakes, therefore keeping them cooler. However, in a car that gives you full manual control, either by a sequential-shift manual mode (like my car has), or… a manual, you can do so much more. Realistically, with manual control, you can use engine braking at any amount deceleration. I, personally, have never had to push the brake pedal beyond halfway, the engine itself is doing the rest of the work. The less you engage the brakes, the less friction they generate, lowering heat, and also, lowering wear. The less I wear out my brake pads, the less often I have to change them, and therefore the less money I spend in the long run changing them.
Additionally, unless you redline the thing, engine braking is not bad for the engine. Sounds of one at 5,000 RPM aside, you’re not doing anything “special,” you’re taking advantage of the natural consequence of modern vehicles attempting to increase vehicle efficiency. Over a certain RPM, some engines may burn a little more oil, but that you can control by knowing when to downshift, and how much you’ll change in RPM when you do. Beyond that, you’re pretty much just adding normal wear and tear, maybe less when you consider that you’re not constantly adding multiple explosions per second into the mix of things that it’s doing.
In the end though, the brakes will stop the car. The engine can just help provide assistance.
So in the end, I see it like this:
|Reduces brake pad wear||Makes weird noises|
|Essentially “free” braking force||Might burn a tiny bit more oil|
|Can be used for speed control too||Requires manual shifting|
|Saves on fuel||(Potentially) one more thing to worry about doing|
|Lowers engine wear a little|
|Forces you to pay attention to what the car is doing|
|Just feels cool|
I only had to resort to one subjective point to fill that table out… one.