Exhaust brakes

[DieselMonkey]

Guys,

i was thinking of starting work on an exhaust brake. Not for the help of down-hill braking, but for quicker warm-ups and i also realised that before shutting down, if the brake was applied, the turbo would run slower also, thus running for less time with no lubrication.

I notice that U.S. Gear's waste-gated system is totally air-tight up until it opens. Does a totally air tight system not sound like trouble ?

I had planned, for when full shut, 3mm clearance at the bottom of the butterfly, and possibly some holes drilled in the butterfly itself. What type of operation would be desirable for the quicker warm ups ?

For shut down, i would leave the butterfly open, wait until exhaust temperature is acceptable and then apply the brake...... give 5 seconds and shut down.

I can see no problem in designing and manufacturing the brake, material choice is simple - 316 SS, Brass, Phos. bronze.... just wanted to know what you guys would think acceptable closure of the system when warming up a lightly tuned AAZ engine.... or is this just going to be an un-necessary use of time !!!

Look forward to some thoughts. Thanks. DM

[Dr. Diesel]

I've thought a great deal about an exhaust brake experiment. In short, I've concluded the following two things:

1. Cool, especially if it made a similar noise to the big trucks.

2. But considering the time, energy and money involved in the giving birth to a fully functional unit, pressing the brake pedal is one Phuc of a lot easier.

Concerning turbo cool down, if you listen carefully to a big truck during exhaust braking, the turbo spins quite rapidly. If I were to hazard a guess, I'd say that like your idea, the butterfly doesn't fully close. (probably to keep from blowing the whole exhaust manifold off) The gasflow out the exhaust ports then is forced through a very small venturi, (past the partially closed butterfly) and is accelerated to very high speeds. (bernoulli's principle) This causes the turbo to spin quite fast. Which, pretty well blows that theory out of the water, even if it could idle with such an exhaust restriction.

[QuickTD]

1. Cool, especially if it made a similar noise to the big trucks.

The cool noise made by the engine brakes used on most heavy trucks would be difficult to achieve. The jacobs engine brake ("jake brake") absorbs power by slightly cracking open the exhaust valves as each piston nears TDC on the compression stroke. This "wastes" the energy that was stored in the compressed air and generates the characteristic noise. As the piston passes TDC, the air has been exhausted from the cylinder and the piston is forced to pull a vacuum on the cylinder. The act of pulling the vacuum also absorbs power and this power is again lost (and more noise is created) when the exhaust valves are opened by the by the cam at the end of the would be power stroke. Naturally, fuel to the injector is cut during the engine braking process.

Most heavy truck engines use unit injectors driven by the camshaft. The unit injector cam lobes provide a convenient method to drive the exhaust valves open near TDC during engine braking. The jake brake uses a simple hydraulic master/slave system actuated by an electric solenoid to connect the injector and exhaust valve rocker arms during engine braking.
 
Unfortunately only the late model PD unit injector engine has the injector cam necessary to actuate a true "jake" brake. The exhaust brake being discussed here really doesn't make any especially cool noises. Some newer heavy trucks (volvo?) that use common rail injection and lack the necessary injector cams, use this type of engine brake. In my experience the operation is fairly noiseless. Having lived next to a busy intersection with lots of heavy truck traffic for the last 8 years I can honestly say i'm happy to see the classic "jake brake" on its way out...

[andy2]

I've installed many aftermarket "exhaust brakes'' on Ford and Dodge diesels and on the 12valve cummins you actually have to change the exhaust valve springs for ones twice as strong . This is a neccesary mod due to the higher backpressure created by the exhaust brake, this pervents any possibility of valve float during higher exhaust backpressure  .Also on the powerstroke to install the exhaust brake you have to first remove a warm up butterfly whitch is basically an exhaust brake that is only used to warm up the engine in cool temperatures, I have a couple of these potential exhaust exhaust brakes sitting around If your interested Quick TD,Dr Diesel all you need is an accuator or some manual controls  :twisted:

[deepmud]

Note that both the factory Ford warm-up brake and the aftermarket brakes are going on "post turbo" - so I guess would slow the turbo faster. The restrictions does give the engine and turbo something to work against when cold, and really does warm up the engine, even at idle in extreme weather (Worked on the Alaska Pipeline comm system at -50 and the Excursions kept themselves toasty - the computer has a monitory of the coolant temp and revs up and works against the restrictor as needed to stay up to operating temp).