tnc110
Well-Known Member
Get on an old john deere diesel farm tractor(any of the old 2 cylinder)....go down a grade....pull the compression release. ...JAKE BRAKE....same principle....
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Ford vs. a Dodge...... (Gooseneck Tow Vehicle)
- Thread starter Canuck Digger
- Start date
Not really but you do get to take advantage of some added friction yes.
chevota84
Well-Known Member
I'm not fighting, I'm attempting to explain how they work but apparently I'm failing. Information directly from jacobs:
A jake bleeds off compression at the top of the compression stroke to steal the return energy out of the cylinder.
The load leash description is much longer but it holds the exhaust valves slightly open during the entire compression stroke to force more air against the closed vgt and create more back pressure.
A jake makes the engine do the braking and a load leash assists the vgt in braking, so definitely not the same principle. Just because they both hold the exhaust valves open at some point in the engine cycle doesn't mean they work on the same principle, the cam also holds the exhaust valves open and it's also not an engine brake.
tnc110
Well-Known Member
Jeez, you boys are really splitting hairs here. What I'm saying is that you do not have to open the exhaust valves at tdc to get additional braking. It's the same PRINCIPLE as a a shock absorber...take a large diameter piston and try to force air or oil through a small opening and you are going to experience resistance. Close the small hole and the shock will kick back....same as a compressoion engine. There is not a special mechanism in a shock absorber that opens the valving at a precise moment. Same PRINCIPLE. Aparantly you dont know the simple definition of the word principle, so i posted it above. But yet it is still being argued. The PRINCIPLE on both compression brakes is that air is being compressed, and is then released so that it does not push the piston back down in the cylinder...this is what we call a principle.
tnc110
Well-Known Member
It is not friction, it's compression. Or the release of.
tnc110
Well-Known Member
Back to the subject at hand. OP said stopping was important to him. Hands down, the Dodge with a manual trans and a PAC Brake Load Leash is going to provide far superior braking than any other set up.
tnc110
Well-Known Member
I'm not fighting, I'm attempting to explain how they work but apparently I'm failing. Information directly from jacobs:
A jake bleeds off compression at the top of the compression stroke to steal the return energy out of the cylinder.
The load leash description is much longer but it holds the exhaust valves slightly open during the entire compression stroke to force more air against the closed vgt and create more back pressure.
A jake makes the engine do the braking and a load leash assists the vgt in braking, so definitely not the same principle. Just because they both hold the exhaust valves open at some point in the engine cycle doesn't mean they work on the same principle, the cam also holds the exhaust valves open and it's also not an engine brake.
If a truck were to be equipped with a load leash only, no vgt, it would still provide engine braking, in the same way that a jake brake does. It does not need the VGT to work. See my example above with the old John Deere....there is no VGT on a 2 cylider deere, I promise you! Yet engine breaking is still achieved, VERY much like a jake brake, might we call it the same principle???
chevota, I'm am sure you know far more about diesels than I do, but you are missing the boat on compression braking.
chevota84
Well-Known Member
No, it wont. It's holding the exhaust valves open for the entire compression stroke so no energy is wasted compressing, it's basically like opening the unloader valve on an air compressor. You don't get any gain from the return energy but you don't lose any energy on the compression stroke. There might be some net energy loss over just coasting but it won't be much.
Birken Vogt
Charter Member
Admittedly I don't know how this particular thing works.
However if you hold the exhaust valves open only a crack through the entire compression stroke then you should get a somewhat comparable energy loss as a regular Jake. Then there is the other benefit of having some air returned to the cylinder on the downstroke.
If I remember correctly, the Mercedes MBE900 had a 5th small valve that stayed open all the time when braking to accomplish this same thing.
Scrub Puller
Senior Member
Yair . . .
Fellers I know nothing of Jakes but I straight up don't understand the following statement . . . .
Any compression release I have used is for the purpose of releasing the compression to make the engine easier to crank.
To take that theory a step further . . . .
We get our Johnny Popper and pull up on a slope where the compression in the cylinders will just hold the tractor on grade . . . we then release the compression and the tractor runs away.
How is that in any way an analogy to an engine brake?
I always thought the most braking you could get out of an engine would be for the drive train to turn the engine against compression with no fuel but apparently the Jakes do much better than that.
Cheers.
Fellers I know nothing of Jakes but I straight up don't understand the following statement . . . .
Any compression release I have used is for the purpose of releasing the compression to make the engine easier to crank.
To take that theory a step further . . . .
We get our Johnny Popper and pull up on a slope where the compression in the cylinders will just hold the tractor on grade . . . we then release the compression and the tractor runs away.
How is that in any way an analogy to an engine brake?
I always thought the most braking you could get out of an engine would be for the drive train to turn the engine against compression with no fuel but apparently the Jakes do much better than that.
Cheers.
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Scrub, diesels are generally of such high compression that when running downhill say, most of the power used to compress the air on the upstroke of the piston gets returned to the piston to push it down once the crank goes over TDC. Not much braking. The original Jake was simple in it's elegance, it simply managed, on demand, to use the mechanical injection rocker to also open the exhaust valves at about the point the injector would usually fire, thus releasing the compressed air to the exhaust so the power is not returned to the piston. A byproduct of that process is the rather unique sound of a truck running downgrade "on the jake". YMMV.
tnc110
Well-Known Member
You are absolutely 100% wrong. This system cracks the exhaust valve .020", if it were to open the valve as much as a cam cycle would(.3xx) then you would be on track. But .020 is small enough to require a lot of force to compress the air in the cylinder, but enough of a gap to allow this compressed air to escape and not force the piston back down. This makes CONSIDERABLE braking force.
Please explain to me how my example of the old John Deere works....I'm not making this $hit up...we live in the mountains....when you take one of these old tractors down a grade and pull the compression release lever the tractor slows down a LOT. We have several old Deeres, and we get a bunch of people together and got on hayrides....we always take a diesel because it is much safer and can hold back going down grades when the compression release is pulled...
so Chevota....please explain this weird phenomenon!
Your compressor theory does not hold water...the unloader valve opens MUCH more than an exhaust valve on a Load Leash system.
chevota84
Well-Known Member
I can't explain it any simpler and it's giving me a headache trying. Read this http://pacbrake.com/mopar-max-magazine-article-on-the-p-67-loadleash-engine-brake/
If you still don't get it, go ahead and tell all your buddies you have a Billy big rigger jake brake in your dodge and be happy about it.
If you still don't get it, go ahead and tell all your buddies you have a Billy big rigger jake brake in your dodge and be happy about it.
tnc110
Well-Known Member
Oh I get it. I get it very well. Simple physics actually. You take a high compression engine and crack the exhaust valves it is going to provided engine braking. Whether it is a 15L+ truck engine, a 6.7 dodge cummins or a a 1958 John Deere 2 cylinder tractor. It is all the same principle, granted each has their own differences. but the principle is undeniably the same. Some people in this world are just too stubborn or proud to admit that they are wrong.
tnc110
Well-Known Member
I suppose for your next trick, you are going to argue that a Ford provides better braking than a Dodge???
mitch504
Senior Member
Yeah, the original poster probably bought a Chevy by now.
Canuck Digger
Senior Member
- Joined
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- Mission, BC, Canada
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So I found my truck! Thought I'd provide some feedback. To combine my business and family needs, got me a 2010 dodge ram 5500 with a cummins/asin. It's a quad cab sitting on the short (and hard to find) wheelbase of 168" I believe, sporting a 9' flat deck with 4 built in under mount toolboxes. 4x4 of course. It's got about 70k miles on it so just broken in. The SLT model is certainly a step down from my laramie, but being on a budget take what I can get. The nice thing about this year truck is it's the last year of pre DEF. The gas milage is awesome. Comes with a factory exhaust brake and came with a flip over gooseneck hitch. Pretty basic truck but certainly plenty of pulling power and versatility...