Diesel Engine Braking

[BucketList]

Hate to keep repeating this but I am new to the forum and RV's and I for some reason need to explain or excuse some of my uniformed questions........

How does the engine braking work on a diesel engine? Depending on the chasiss manufacturer, they call their braking systems by different names such as:

2 stage "Jake" compression brake
or
"VG" turbocharged and ocmpression "intebrake"- two stage high low

[Steve Ownby]

I don't think you should feel the need to be apologetic about your questions as few of us were born knowing these things. If you give your specific situation it will enable others to give info that is correct for you.

1. Jake brake or compression brake: This was developed by the Jacob's Company as an add on for over the road diesel trucks and was so universally accepted by truckers that it became a standard part of many diesel engines. It is internal to the engine and works by changing the exhaust valve timing so the high diesel compression will retard the forward motion of the vehicle. The high/low switch determines how many cylinders are effected.
2. Exhaust brake or PAC brake (a major manufacturer): This is a switch controlled butterfly valve down stream of the turbo which creates exhaust back pressure which retards vehicle motion.
3. VG turbo: Veriable geometry turbo was developed around 2003 to help Cummins meet EPA goals for 2004. This turbo can be electronically controlled to accomplish much the same thing as the above exhaust brake.

The true Jake brake is found on Cummins engines ISL, ISM, ISX and Cats above the C9. I assume all Detroit Diesels. I don't know about the Maxforce.

Exhaust brakes or VG turbo type brakes are generally found on the smaller displacement diesels.

The above is a general simplified overview and is not intended to be exhaustive as there are exceptions (all ISL's are not equipped with Jakes).

[Route 66]

Jacobs exhaust brake

Jacobs engine brake (compression release)

[Mr_D]

Originally Posted by Steve Ownby

I don't think you should feel the need to be apologetic about your questions as few of us were born knowing these things. If you give your specific situation it will enable others to give info that is correct for you.

1. Jake brake or compression brake: This was developed by the Jacob's Company as an add on for over the road diesel trucks and was so universally accepted by truckers that it became a standard part of many diesel engines. It is internal to the engine and works by changing the exhaust valve timing so the high diesel compression will retard the forward motion of the vehicle. The high/low switch determines how many cylinders are effected.
2. Exhaust brake or PAC brake (a major manufacturer): This is a switch controlled butterfly valve down stream of the turbo which creates exhaust back pressure which retards vehicle motion.
3. VG turbo: Veriable geometry turbo was developed around 2003 to help Cummins meet EPA goals for 2004. This turbo can be electronically controlled to accomplish much the same thing as the above exhaust brake.

The true Jake brake is found on Cummins engines ISL, ISM, ISX and Cats above the C9. I assume all Detroit Diesels. I don't know about the Maxforce.

Exhaust brakes or VG turbo type brakes are generally found on the smaller displacement diesels.

The above is a general simplified overview and is not intended to be exhaustive as there are exceptions (all ISL's are not equipped with Jakes).

Pretty good in my book!

[David K]

My 2002 Cummins ISC 8.3 is equiped with a Jacob brake which is external to the engine. It is located on the engine side of the turbo. It has the butterfly valve referenced above but, is not a pac brake. It is a Jacob brake with Jacob stamped on the air cylinder which closes and opens the butterfly.

[crah]

Originally Posted by David K

My 2002 Cummins ISC 8.3 is equiped with a Jacob brake which is external to the engine. It is located on the engine side of the turbo. It has the butterfly valve referenced above but, is not a pac brake. It is a Jacob brake with Jacob stamped on the air cylinder which closes and opens the butterfly.

That is an exhaust brake as well. Just happens to be made by the Jacobs system company instead of PAC.

[336muffin]

On my 2003 American Dream I had a real "Jake Brake " inside the head on the valves now I have a Cat with the exhaust brake, big difference in stopping power.

[Gary RVRoamer]

The Jacobs brand exhaust brake is not the same as the well known "Jake brake", which is the Jacobs internal engine (compression) brake that crah described in his excellent summary.

There are several manufacturers of diesel exhaust brakes, but "Pac brake" is often used generically for them, just like "Coke" is used for cola drinks. BD, D-celerator (US Gear), and Banks are some other brands.

[EngineerMike]

I have the 2-stage Jake on the head (each stage is 3 cylinders, so 1-2-3 and 4-5-6). I also have the VGT braking. The combination is considerably different in feel from the 05 engine build (o6 model year coach) we had previously. The 06 coach would require fuel to maintain 20mph downhill on a 12% grade; the 08 needs service brakes to hold 20 on that same grade. And there is only slightly perceptible difference between Hi & Lo stage when selected; Hi is just a teeny bit more braking than Lo. I've had it tested w/valve cover off to assure both were working, as that's how little difference there is. My guess as to why VGT +6 cyl engine brake is only a teeny weeny bit more than VGT +3cyl is that the VGT is essentially an exhaust brake muffling the engine brake. In other words, VGT is not fully additive to Jake, and VGT is fully engaged regardless of Hi or Lo selection.
At any rate the overall effect is that same weight coach, same frame, wheelbase, tire size, gearing, etc., and 08 rig w/combo engine/turbo braking (07 engine year w/DPF) does not stop as well as the 06, but 08 stops OK.

[RustyJC]

Originally Posted by Gary RVRoamer

The Jacobs brand exhaust brake is not the same as the well known "Jake brake", which is the Jacobs internal engine (compression) brake that crah described in his excellent summary.

Although I recognize the difference as well as the colloquial use of the term "Jake brake" to mean a compression brake, be aware that Jacobs markets their exhaust brakes using the Jake Brake name. My 2002 Dodge Ram with the Cummins ISB 5.9L had a dealer-installed Mopar/Jacobs exhaust brake in place before I ever took delivery - the decal in the back window of the truck that came in the box touted the presence of a Jake Brake.

Rusty

[Mekanic]

Originally Posted by 336muffin

On my 2003 American Dream I had a real "Jake Brake " inside the head on the valves now I have a Cat with the exhaust brake, big difference in stopping power.

AND? which one worked better?

[336muffin]

OK, I had a Jacobs engine brake in my American Dream which works much better than a exhaust brake.

[dieselbeaver]

To compare "engine brakes - either internal or external" one needs to look at the "retarding HP" listed by the manufacturer. Generally speaking a compression brake(under valve cover) will always have greater retarding HP. An exhaust brake(not under the valve cover) will only produce a percentage and it is governed by the amount of back pressure a given engine can handle. And example would be that most of the 5.9 cummins were limited to 60psi back pressure and that is governed by the valve springs among other factors. That generally equates to approx 150 hp at rated rpm. That's the other catch on both types.....it takes rpm to make them function and more is better. That's why your Allison downshifts out of 6th to 4th. The compression brake can have over 300hp on the big Cats, Cummins, and Detroits.

Take a few minutes and explore jacobsvehiclesystems dot com and or pacbrake dot com. Just understand that not every engine has the option of one or the other.... Most sub 10 liter engine across the board will only have an exhaust brake as an option - even that has an exception in the 07 and newer ISC, but their under valve cover compression brake is weak.

Just some more food for thought,

Allen