Exhaust Brake?

[Hammer]

Let's look at the case where the intake is open, exhaust is closed, and the piston is on the downstroke. The pressure in the chamber is 15psi less than atmospheric. There is then 15psi pushing on the bottom of the piston (crankshaft side). Yes, it takes energy to do this but once the intake valve closes, the 15psi on the back side of the piston pushes back with an equal force on the upstroke. It is a reversible process.

That works in a single cylinder engine with no crankcase vent.
You ever pull the PVC valve and see how it PUFFS the air out? One for each cylinder like you are describing.
Two things are different from your scenaro though, the PVC allows vacuum to pull out pressure from the crankcase. And for each piston on a down stroke, there is another on the up stroke, which balances (not perfectly, I know,) the pressures in the crankcase fairly well.

What you are thinking of is a two stroke single cylinder engine. Where that same pressure under the piston is actually used to force air into the cylinder.

A 4 stroke engine does not have a sealed crankcase, and will not create ENOUGH pressure against the underside of the piston. YES, it does create some, but not enough to balance it out, or any where near close enough.

Back on topic, exhaust brakes.
Love the one on my pickup! I have over 192k miles on the original rear brake shoes, and they still have decent life left in them! Only changed the front pads twice, and still the stock rotors (2001 dodge 2500.) So you can see just how much it has extended the life of my brakes, and by extension, lessened the wear and tear on the entire brake system.
I was driving a KW with a Cat C15 with Jakes recently. One hill I was on was a 14% grade. Sure made that hill a LOT easier on the brakes, and made me feel like I could really use them if I still needed to.

Biggest question on the deuce is how much back pressure can you safely run with the stock exhaust valve springs? When I looked, I could only find a reference for 25 psi. Which is decent, but not like the normal 60 psi that most systems can create.

 

[Kohburn]

I think the last thread about it said that the springs should be able to handle 65 so 50 would be a safe bet. One guy is running 35psi, I think I would start there watching the pyrometer and try stepping it up a little at a time. I would be real happy being able to run 45psi as that's still ~twice the engine braking force of a throttle plate on a gasoline engine.

my only real debate is how I want to activate it - plannign an electronic driven valve, but how to switch it.
-do I want to just have a manual hand switch
-do I want it to be linked to the brake pedal with a manual override activating in the first inch of pedal travel.
-do I want it to be linked to the gas pedal with only a manual over ride. activating anytime i release the gas completely

I know that some trucks activate from the gas pedal to fascilitate faster shifting, don't know that I would want to do that but i could use the manual override to turnit off when i didn't want that function.

my inclination is to use the soft part of the brake pedal travel to activate the exhaust brake, i would then have to press harder to activate the hydraulics. doing it this way is a bit more natural and intuitive.

 

[Hammer]

Have a simple micro switch on the throttle pedal. Have it ONLY activate when there is NO throttle pressure.
This is the way they are set, and one of the best ways for them to work.
Have a switch that turns the entire system on/off. So it isn't always running the brake when you don't need it. They can be pretty noisy when you are just idling in traffic, etc.
I have my manual switch for mine on the shifter. I found an old truck in a wrecking yard that used an electric splitter instead of air. So it looks and works great!
That way I can leave the brake off when I don't need it, but can easily and QUICKLY reach it.

 

[GregSLSTJ]

I'm reviving this thread as I had some people asking about my exhaust brake so here is what I did. I do have to credit cranetruck as I was inspired by his idea.
I used a 3 3/4" wabco exhaust brake from a 2001 Kodiak truck that had a cat 3126 engine. Not sure of part number.
Ingersoll Rand 3 way 1/8" 12vdc solenoid valve - 6JJ52
Enclosed Limit switch top actuator SPDT - 3XG60
lighted toggle switch.
oil pressure gauge to monitor exhaust back pressure.
So the switch on the shifter sends power to the limit switch that is mounted under the accelerator pedal this controls the solenoid valve that actuates the air cylinder on the exhaust brake. The air cyl. is spring loaded so it needs air to close the valve. When you let off the pedal it automatically actuates the brake and when you get back on the gas it turns the brake off. The pressure gauge just shows the back pressure so you know if it goes to high. I think 30 psi is safe for our engines. It works pretty good you can feel it when you get out of it above 1800 rpms. But I wouldn't put this modification to high on your to do list..it's no engine brake (jake).

 

[w3azel]

Am I missing something here. I can most certainly down shift my truck to slow it down. I've never had the rpms climb on me when I'm not of the accelerator going down a hill. Sure it goes up when you down shift but its a very noticeable braking force to slow the truck down. I just drop the rpms down to around 1600 push the clutch in down shift bring the rpms back up to 2200 and as I let out the clutch bring the rpms back down. I watched it today to make sure I'm not crazy and the rpms never got close to 2500. I only used the brakes for the last little bit of stopping at the light. Used this technique when I went through the mountains of WV. Maybe I'm missing something or I have something wrong with my truck.

 

[Jeepsinker]

I slow mine by downshifting as well, only ever use my brakes once i get down to about 5 mph to do the final stopping.

 

[oddshot]

I slow mine by downshifting as well, only ever use my brakes once i get down to about 5 mph to do the final stopping.

Drive at the speed and style you can afford.

Brakes are cheaper than engines, clutches and transmissions. Also easier to repair.

Downshifting to slow down after a lifetime of driving sports cars was a tough habit to break ... but I only use engine braking when driving my MGB's now.

 

[Hammer]

On a more modern vehicle, sure, replace the brakes more often.
Coming down STEEP hills with sharp switchbacks, I will take any auxillary braking I can.
I doubt any of us will truly use the lifespan of these engines, so I think shortening it by however much is a fairly moot point.

Biggest thing, I DON'T TRUST the stock brakes on these, especially in a brake failure situation.
Of course the deuce slows down much better then my 818 with big tires. But I have driven in plenty of places where just gearing it wasn't enough to keep a good control on the speed (and I am talking about already driving pretty darn slow! )
And after driving truck for enough years, I swear by engine brakes and exhaust brakes.
But, to each their own.

 

[cranetruck]

Engine braking is done all the time, especially with a gasoline engine, which has a throttle to provide the resistance to piston movement.
The diesel engine is "wide open" and needs a valve of some sort to offer this resistance to piston movement, either intake or exhaust. Examples are the "Jake" brake or the exhaust brake.
Other methods of drive line braking include electrical and hydraulic, acting on the drive shaft down stream from the engine.
I liked my exhaust brake and used it on long downhill runs with heavy loads.
Remember that you are braking via the differentials and any loss of traction on one side of the truck will result in uneven braking and possible loss of control. Don't use drive line braking on ice or slippery roads.