Jake brakes were never my specialty, and I haven’t worked on a diesel engine (or any engine, frankly) in almost a decade, but if I remember correctly it basically breaches the cylander at the point of compression so that the force goes out of the engine instead of transferring to the driveshaft. I’m possibly completely misremembering though, just putting myself out there to draw engagement and be corrected because I’m curious.
Modern diesel engines have a lot of things in the exhaust system to reduce emissions (turbochargers, exhaust gas recirculators, particle filters etc) which restrict the flow of gas through the exhaust and creates back pressure which adds some engine breaking effects.
Some engines also have an exhaust value to restrict exhaust flow to add more engine breaking, or jake breaks as another poster says.
If you drive an old diesel car, the engine braking is terrible / non-existent. Pretty much every modern diesel has a turbo that restricts the exhaust to provide some engine braking. Some trucks have specially designed turbos that adjust their vanes while braking, and redirect some exhaust back into the intake to increase engine braking. Others have a valve that blocks the exhaust pipe. I don’t think jake brakes are common on anything smaller than a class 7 truck.
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