Engine, Brake, Mufflers Required

I always laugh when I’m driving around Colorado and see the signs that say, “Truckers Engine Brake Mufflers Required.” The sign is clearly another example of the Illuminati’s proviso against any sort of punctuation on road signs. I can forgive the missing comma or colon after “Truckers,” as the sign does separate that word with a bar and a yellow background, but I always wondered whether the sign was saying that engines, brakes, and mufflers were required (duh), or whether there could be something as bizarre sounding as an “engine brake muffler.” Brakes are for wheels, not engines, of course, and mufflers are for exhaust not brakes, so the three make no sense together.

Now, perhaps one of the out-of-work hyphens I mentioned in my last post could be put to work here and clarify that there is such a thing as an engine-brake. Because there is. I had no idea.

I engine brake (verb) every day, it’s one of those things you learn to do when you drive stick and prefer to avoid the brake at all costs. I’m a master, and I drive my 5-speed Jeep Cherokee as if it were a Maserati, driving down winding mountain passes with nary a red light beaming behind me. But I had no idea that “engine break” was a noun as well as a verb.

Engine braking is when you down-shift without applying the gas causing the engine speed to be out of balance with the angular momentum of the transmission’s flywheel. Many novice manual drivers forget that, against intuition, you need to apply more gas to down-shift and less gas to up-shift because higher gears are more efficient at a given RPM and speed. They’re the ones you hear grinding and whizzing and stalling down your block.

When engine braking, the flywheel is spinning too slowly in relation to the engine and thus causes an increase in resistance against the engine. The pistons to have to push harder to compress the air gas mixture and the temperature of combustion increases due to the increased pressure and that heat is exhausted out the back and into the engine’s liquid cooling and out the radiator. The increased resistance against the flywheel and clutch plate also dissipates into the air as they spin.

This form of braking isn’t just a fun diversion for manual drivers who don’t want to flash their brakes, it’s more efficient and prolongs the life of the car and its components. Any sort of braking is going to cause friction and thus heat and thus distortion and thus uneven ware, but engine heat is preferable to brake pad heat because the engine is designed to easily dissipate that heat into the atmosphere and away from critical parts that can warp and break. The engine has liquid cooling, a radiator, and lots of air flow; the brakes do not.

There’s another advantage to engine braking as well, you maintain steering and power control. Many accidents are caused by panic breaking, the brakes locking, and subsequent loss of control. An astute driver would have accelerated around and away from the collision. Down-shifting during engine braking gives the engine more leverage against the road and the road less leverage on the engine. The former ensures precision handling, the later eases stress on all parts of the car.

This effect is easy to accomplish in any car (simply down-shift at the opportune time) automatic or manual, and you need not have a physical “engine brake.”

But large (diesel) trucks do use a special device to specifically increase the effectiveness of engine braking, the eponymous “engine brake.”

The engine brake is used in large diesel vehicles because the dissipation of momentum into easily-dispersed heat is less efficient than in gas engines and the mechanics of the stroke cycles don’t allow for the counter force effect. The engine is already much hotter and the compression is already greater (so much so that diesel engines don’t use spark plugs to ignite the air fuel mixture, it ignites by itself due to the ambient engine heat and the greater pressure).

So an engine brake can be installed to allow a diesel engine to operate like a gas engine. The only problem is that it’s loud as hell. Thus the need for a muffler to quite it down.

So, when the sign says “Engine Brake Mufflers Required” it’s to prevent noise pollution while allowing truckers to exploit the benefits of Engine Braking:

Now you know.

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