Jake Performance

[TerryB]

This is something I just can't quite wrap my head around and I think I should be able to. Talking about jake brakes and their performance and why some have more holding force than others. What is it about the systems that make some work better than others? Not asking how a jake works, but why some perform better than others. The truck I drive has a CM570 in it, the jakes "work" great. I've never driven a truck with that strong of an engine brake. But to be truthful, I haven't driven many of "todays" trucks, especially not loaded. My previous truck had the 12.7 Detroit, the jakes weren't even close to as strong as this CM570. Now I understand that's not comparing apples to apples, but what is the biggest reason for the difference? Displacement? I've had several trucks with the N14 in them and even back to the Big Cam III days, I sure don't remember the jakes being this strong. I'm sure electronics play a big part of it, but is that the major difference? Does the timing change when jakes are applied? I would imagine the VGT turbo plays a part on the engine that have them, but like the CM570 just has the waste-gated turbo. Not having any problems, just trying to understand.

[Bengy88]

Everything about the engine plays a part. The piston size, the piston stroke, valve size, electronics, duration, timing, adjustment, turbo style.... Etc. Its kind of like saying why doesnt an 290 cummins pull like an x15.... Its 2 completely different worlds

[TerryB]

(12-22-2022 )Bengy88 Wrote:  Everything about the engine plays a part. The piston size, the piston stroke, valve size, electronics, duration, timing, adjustment, turbo style.... Etc. Its kind of like saying why doesnt an 290 cummins pull like an x15.... Its 2 completely different worlds

Yeah I understand what you're saying. Maybe the thing that makes it a little harder to understand, for me anyway, is that we don't have fuel in the equation. Fuel and Air at the right time make power, we don't have fuel so know the Air is making the "power", to an extent.

[Rawze]

BTW: That 570 with its waste-gated turbo is actually weaker than just about anything newer (engines with electronic turbo's) on the jake brakes.


The reason why the newer red engines have a stronger jake is in fact the VGT electronic turbo + the jake design of the enigne vs. other engines.

Red engines literally have the strongest jake brakes in their class, and the red engine maker used to advertise this a lot, years ago.

and .. NO, there is no fuel being applied, so NO, there is no 'injection timing' or any other type of firing of the cylinder involved, etc.


What is different about the red engines is that it uses the electronic turbocharger to choke the exhaust manifold to block off up to 90% of the exhaust flow. After it does this, what it does next is the part that is unique to cummins ... even on the old 570, although it is not as good at it due having no VG turbo ...

So ... It traps and compresses the air in the cylinder(s) like any other engine does to make extra resistance to the fly-wheel ... but it does something different before releasing it out the stacks.

When that compressed air is released finally into the exhaust manifold, the red engines traps a big portion of it there (using the turbo itself to choke the manifold), and opens a second exhaust valve to transfer it into a second cylinder .... and then compress it again, amplifying the amount of air into that second cylinder quite a bit above what normally would have been able to be taken in via the intake alone.

It is a pretty unique trait to cummins engines.


By the way .. rear end ratio plays a big role in how strong the jake is on an engine too. The higher the ratio, the stronger the jake is... Ie >> a set of 4.11's will be quite a bit stronger in holding power than a set or 3.27's. This is yet another reason that these newer heavy haul trucks need to be geared right instead of some garbage, engine killing, fleet-spec' tall rear ends.



-=== related to engine brakes on newer engines, since we are on the topic ... ===-

This double-compression engine brake design can also be a huge problem if someone has a bad-delete program shoved into their ecm. More than 90%+ of all delete programs are bad.. and about 40% of those, some completely clueless moron who made that program also fumbled around with the jake brake settings "in attempts to make them stronger". This is a massive no-no.

On newer trucks with VG turbo's, It is almost always those guys who have abnormally tall rear ends vs. the loads they carry, that complain about the jake feeling 'weak' from the factory. Because of this, many of these so-called 'tuning' idiots are quick to try to make up for it in the programming out of sheer stupidity.

By choking the exhaust/turbo harder than it is programmed/intended for (usually editing the turbo engine brake maps in the programming), then that highly compressed air will cause extra exhaust valve closing delay when the valve does open. This sets the engine up to easily allow for a piston strike a valve at higher rpm ranges and the engine brake on max. This destroys the engine very quickly, and I have seen this done to them many times over the years + the aftermath.

[TerryB]

(12-23-2022 )Rawze Wrote:  ...

Rawze, thanks for this explanation. I really appreciate it.

[tree98]

Seems like the amount of back pressure on the VG from a fully loaded 4.10 rear truck on stage 3 jake would destroy it in a short time, that's gotta be an incredible amount of pressure. I guess they got it figured out.

[Rawze]

(12-23-2022 )tree98 Wrote:  Seems like the amount of back pressure on the VG from a fully loaded 4.10 rear truck on stage 3 jake would destroy it in a short time, that's gotta be an incredible amount of pressure. I guess they got it figured out.

It is not that extreme actually ... on most ISX's, during jake, it is about 28 psi on the intake, meaning that it will be holding back about 44-45 psi on the exh. manifold to put into the second cylinder. Some people are reporting the intake pressures are slightly higher (factory programming) on the new x 15's, but I have not seen consistent solid data on them yet myself.