Exhaust brake

[stefos]

[color=red>The magic word was "exhaust brake" wich made the travel possible.</U> When I came back I saw the new forum. I have to learn some things but it is Ok. This is a great development. Thank you.[/color] [color=#0>kkjjk</FONT>
<FONT][/color]

[color=#ffff00>I][/b] to repeat it here because I was so pleased with the exhaust brake that I want to tell it to others. It isn't something new. It was there since I bought the truck and it is a part of the Greek army convertion which made old gassers to Steyr Diesels. The new thing is that it was the first time I had to travel on high speed with more than a ton of payload on the highest Greek mountain pasages using forth gear and allmost no use of service brakes. If there wasn't the exhaust brake I would have to change one or even two gears down to go dounhill safely and not overheat the brakes. I think that Exhaust brake is a must have convertion for the Deuce on a hilly terain.[/color]

 

[spicergear]

An exhaust brake is a great idea on diesel engines. A gas engine has vacuum when you lift off the pedal as the butterflies in the carburetor close that creates a vacuum above the pistons and that vacuum slows the speed of the engine as it wants to hold the pistons up in the bores and not let them down. A diesel has no butterflies which regulate airflow, they are wide open all the time and are solely controlled by the fuel injected. Even though a diesel engine usually has roughly twice or more times the compression of a gas engine, the lack of intake vacuum makes them poor compression brakers and why you can have a run-away situation on hills...well, a contributing factor anyway. Exhaust brakes are simple butterflies in the exhaust that are closed or at least tipped in to slow the flow of exhaust and build backpressure into the engine. What that does is creates backpressure into the cylinders on the exhaust stroke which causes the engine to have to force out the exhaust against pressure and in turn slows the engine speed. Simple and effective. There are a couple of things to keep in mind if looking into this. I've seen where a pressure gauge should be plumbed into the manifold so that one can keep an eye on pressure build up, or the butterfly should only be able to hold back a certain amount of psi in the exhaust. Some engines will only take 30psi backpressure to lift the exhaust valves off their seats. That could possibly cause a piston/valve interference issue which would really suck. Also, don't confuse this type of exhaust with a "jake" brake, invented by a guy named Jacobs. The Jake is usually a hydraulic/mechanical operation inside the engine that opens the exhaust valve on the compression stroke and burps out the explosion from the power stroke, then closes to cause a slight vacuum effect. That's why trucks rumble so loudly when on the jake as it's basically throwing the explosion into the exhaust instead of using it's power to push the piston down.

 

[Desert Rat]

SG,
Excellent synopsis!

 

[Recovry4x4]

30 PSI is what the max recommended exhaust pressure for the multifuel. My recent visitor, Bjorn Brandstedt has one on his deuce and has pressure gauges to monitor the backpressure.

 

[rdixiemiller]

So, Is this a kit you can get? Or something you fab in the shop?
Regards

 

[stefos]

When I started this I couldn't hoppe that I was about to learn so many interesting things. In the begining my
main fear was that the exesive use of the exhaust brake would harm the propeler shafts or something else in the drive train. I also thought that the butterfly could melt. This is a bit dificult because when the butterfly closes the system also cuts the fuel. But now you mentioned, a 30psi backpressure in the exhaust manifold would give the ex valve more than 50 pounds of force in the direction to open. This will overcome the valve spring tension and open the valve or not let it close when the piston is up. Aou! On the oposite site exhaust brakes are very common on heavy trucks and I never heard of an engine problem so I have to repeat the old saying: " God gives nest to blind birds"(Greek). I am about to conect a gauge to monitor the pressure. I can only think about a turbo pressure gauge. Do you find it right?

 

[Recovry4x4]

Bjorn did some research with Hercules and came up with that 30 PSI from them. He scavenged an air operated valve from a junkyard somewhere and fabbed it into the exhaust. It looks really simple and he says it makes a big difference. After seeing his, I'm somwhat intrigued!

 

[spicergear]

30psi doesn't sound like much pressure for a valve until you consider all aspects. Lets say the valve is 2.00" diameter with a 3/8" stem. The equasion for figuring out the area of a circle is Pi x radius squared. for the 2.00" valve would be 3.14x 1x 1= 3.14sq" The stem has .11sq" area. 3.14- .11 = 3.03sq" So that's 3.03 square inches of area on the top of that valve that the exhaust is pushing back on. Doesn't seem like much until you figure that original 30psi number is for ONE square in. and now it's got over 3 square inch to push back on. Just taking a glance in the Summit catalog they have some replacement springs "...to restore performance over 3500rpm..." with only 89Lbs seat pressure.

I gotta start drinking more.

 

[Desert Rat]

SG,
You're dead on again. You sure you don't have a Masters in Engineering from Pitt. or somewhere?

 

[spicergear]

Heh,heh...nope, I don't sleep well. Surprising the clearity of thought at 2am as the hot water rushes though the plumbing and thousandth sheep jumps over the fence.

 

[Desert Rat]

SG,
Sometime when I have a summer off and am not preparing for another major move I'd love to see your truck and pick your brain on a bunch of different ideas I have for my baby.....

 

[spicergear]

Anytime man!

 

[Desert Rat]

SG,
Cool! I'll let you know when the family is headed that way.

 

[cranetruck]

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[liljohn]

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[cranetruck]

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[stefos]

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[cranetruck]

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[rdixiemiller]

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[stefos]

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