For those on the 1/2 ton vs 3/4 ton bubble...

jaycocamprs wrote:

rhagfo wrote:


Well in a gas engine there is a throttle plate when that is closed the engine can't draw combustion air in so the engine has resistance to turning. We called this "Compression" braking, but in reality it is "Vacuum" braking as the piston can't suck in air with the throttle plate closed.

Diesels don't have throttle plates, as engine speed is determined by the amount of fuel injected into the cylinder.

In a diesel it is "Compression" braking as the path for the exhaust is greatly restricted, and when the piston is trying to expel the exhaust gas it is blocked offering great resistance to piston travel.

That's still not "Compression braking". Compression" braking is when the piston compresses the air and it’s then dumped by opening the exhaust valve. Before the piston travels back down.

Well I am going to ask understanding to what I am about to write. Please understand I am ambidextrous so I sometimes I have arguments with myself.

I stand by my first statements, gas engines have throttle valves that control flow of air into the engine. when that valve is shut it can't draw air into the cylinder during the intake stroke, it is pulling a vacuum, this is where the resistance to turning is coming from. During the compression stroke, it doesn't have much air to compress.

Diesels have no throttle plate, so free to draw in as much air as it wants. There for it has compression braking without an exhaust brake, BUT because it id direct injection even at idle it turns the engine partly overcoming the compression.
An exhaust brake places the restriction on the exhaust side, once that restriction is in place the extra effort to push out the exhaust gas past the restriction, resulting in compression of the exhaust gas slowing the engine.

Just think about it for a bit. :B