Engine Compression Brake - Anyone upgraded to 6 position?

[xtechgeek]

Just wondering if it is possible to upgrade the 3 position selector on the engine compression brake to a 6 position selector to get better tuning when descending long mountain grades?

We've taken the coach over the mountains nearly 20 times now and it would be really nice to be able to pick a value between high and medium!

[Dale & Mark Bruss]

The Jacobson Brake on a diesel reverses the valves on pairs of cylinders. That is why there are three positions on a 6 cylinder diesel.

To your answer, no. But think of how much better it is to be switching between 5 and 6 cylinder braking than to ride your brakes.

[rvbusguy]

Liberty Coach and the old Foretravels run a transmission brake.
That's the only 6 speed brakes I know of.


Guy & Helen
16 Cornerstone B

[xtechgeek]

My Cummins ISX 15 manual for my Cornerstone 45k states that the selector can be either 6 position or 3 position. With the 3 position giving 33%, 67% and 100% engine braking power. The six position giving 17%, 33%, 50%, 67%, 83%, & 100% engine braking power.

However, it looks like a Spartan chassis configuration issue. I was just hoping their was a way to upgrade my coach to use the finer settings.

[Cruzer]

While the mechanical mechanism maybe wouldn't need to be changed, it would undoubtedly require a reflash of the ECM and a new switch and wiring harness at the very least. The ISX is somewhat unique in that it couples the engine burn with the valve oriented compression routines. The ISX engine triggers the fuel injectors three times per cycle. A pre-burn flash goes out just prior to top dead center to start the fire going. Once at TDC the second (and largest) flash goes out to push the piston down. A third "chaser" flash fires later on the way down to keep the pressure up for the remainder of the power stroke. That triple pulse injector timing contributes greatly to the efficiency and power of the ISX.

When the engine brake deploys, the system sends a heavy squirt on the up stroke, well early before TDC. That causes the piston to have to compress against a valve that isn't open, severely putting the brakes on the engine. The modified injector timing and pulse during engine braking gives the ISX a ton of braking horsepower. Most engines offer a portion of braking horsepower in relationship to output horsepower but the ISX achieves a complete 600 braking horsepower as well as 600 output horsepower.

Driving down steep slopes, like 10% Teton Pass, with the Cornerstone was a piece of cake. I'm glad it has three steps compared to the two steps I had on our last MMGT with ISL. But with the super braking power I do find myself switching between low, medium and high to regulate the speed. While not really necessary, six levels of engine braking would be nice to have. At least as long as I don't have to spends too much time fiddling around trying to find the right setting before the grade is over.

[DSL417]

Agree...I've done a lot of mountains in the last six months in the Cornerstone. The stages did everything I needed. I found the transition between the levels easy when I needed the most and adequate when the grades were 5% or less. The major thing I needed to do was get off the spread control when working these grades as the brake will not engage till 10 mph over the speed limit...I found that waiting till I was going 75-80 mph was excessive, so when I start the grade I cancel the speed control and use the pedal of and on with the speed brake when I need it.

[Gary.Jones]

Dave

75 to 80 MPH heading downhill in the Rockies was I understanding that right?

Gary

[DSL417]

When you don't use it on a grade, it doesn't take these beasts long to accelerate...heck no, not on purpose, but you're focused on traffic and curves, and you look down and that 5% grade has you pushing 80. But you also have to understand, running 70 in hilly terrain is nothing for the 600 HP ISX. It glides. If it hasn't happened to you, then you weren't looking at the speedometer. JMHO

[Anthem46]

I came down from Flagstaff AZ. to Phoenix AZ. 18 miles of down hill. I do not remember the grade but I never apply my foot brake. VERY HAPPY with the 3 selection.

[DSL417]

Doesn't have to be the Rockies either...there is a 5% downhill on I35 NE of Emporia (there is a cow loading facility in that area for those of you who know!) for about two miles. Speed limit is 70mph. I don't even have the Engine brake on in Kansas, except for there. It is straight and the first time, looked down and speedometer read 85mph. use the engine brake in that area now, for sure.

[Ann n Gene]

My jake brake when cruise control is on engages at 6 mph over set speed. And yes that beast will handle hills and big grades at a much higher speed than you thought you were going if you don't look down frequently. They really ride smooth and just glide. JMHO


2016 Cornerstone 45B
Formerly 2011 & 2013 Anthems and 2015 Cornerstone
2014 Lincoln MKT towed

[jestal]

A true Jacobs engine brake holds the exhaust valve open continuously to dramatically increase pumping loss thus creating the engine braking feature. That is why big trucks with true jake brakes are so loud in the exhaust when they are on the jake brake.

The Cummins engine in the Entegra does not have a Jake brake. It has a simpler backpressure valve in the exhaust to dramatically increase the backpressure to increase engine pumping loss and load the engine more to increase braking. It is very effective but technically not a Jake brake per se and it is not noisy like a true Jake brake either.

[DSL417]

That's why, to avoid this inevidible argument, I simply refer to it as an engine brake. But here it comes!!!!

[loisjop]

Originally Posted by DSL417

That's why, to avoid this inevidible argument, I simply refer to it as an engine brake. But here it comes!!!!

You are correct Dave.
As far as I know every engine Entegra uses for a mh has a true Jake brake. Some control three cylinders per switch position. The isx controls two cylinders per position. Noel