cummins bc vs. cat

Yes 346 Jakes are marginal.
349 were alot better but had issues with wear on the jake heads.

Now a jake and retarder together now you got something.

 

A retarder uses engine oil in a housing that bolts between the engine and transmission. Basically you turn on the retarder and a seperate oil pump in the engine forces oil into this housing. Inside that housing is a turbine assembly that causes drag when pressurized oil is piped into the housing, causing a braking effect.

Jake brake uses a special housing that bolts on top of the head. When actuated, the solenoids allow engine oil into the housing, which creates a hydraulic circuit between 2 pistons. 1 piston (master) is actuated by either a dedicated cam lobe or the fuel injector lobe. The slave piston is actuated through hydraulics and opens the exhaust valves when the cylinders are at top dead center. (There needs to be a set of pistons per cylinder). By opening the exhaust valves at TDC, you are compressing air (absorbing energy) and once the exhaust valves are opened, you have released that stored energy in the compressed air, preventing it from pushing the engine's piston's back down.

An exhaust brake is either a butterfly valve behind the turbo that restricts exhaust flow or it could utilize the variable vanes of a VGT turbo to restrict flow.

 

A retarder should be silent because as northern said its pumping oil into a housing with a spinning impellor in it. I've never driven one so l might be completely wrong though

 

From what all the old school guys told me a million give or take depending on a lot of things.
Forgot to mention earlier on the price thing that a clean 379 with a B model is highly sought after, I see them bring $20ish thousand all the time, but of course I about had to give away my FLD with a Cat just because it was a Freightliner...Sold it for $9k and you would never find a more mechanically sound truck. I would have driven it to Mars. A 379 in the same condition priced at $15k would have had buyers lined up fighting over it.

 

Retarder makes a bit of a whine sound but its usually pretty quiet.

 

Learned something today. I always thought the exhaust valves were held open throughout the entire 4 stroke cycle, using only pumping losses to slow the truck. Thanks Northern.

PS. Do all brands of engine brakes remain closed except at TDC?

 

You would get some braking by leaving the exhaust valves open full time but its much more effective to absorb energy by compressing the air, then dumping it before it has a chance to put a downward force on the piston.

Not sure what you mean by staying closed except at TDC? Valve train will function normally as if you were coasting, the only exception being that when the jake is on the jake/injector lobe on the cam will be opening the exhaust valves one extra time during the cycle when the fuel is normally injected.