Exhaust brake

[Ricky]

(06-05-2021 )Rawze Wrote:  

(06-05-2021 )Ricky Wrote:  ...
So Rawze, is there a too much on the boost when jakeing hard?.
...

The ISX uses the turbo to set the strength of the engine brakes. If it is set too strong then it can lead to disaster in a hurry for someone.

If someone's engine is de-mandated and has bad delete programming, it is often the case where some jerk-weed jacked with the engine brake settings. If so then Yes.. it can drop a valve during heavy jake operations + high rpm, due to valve closing delay caused by excessive exhaust back-pressures.

Newer engines with their higher compression ratios cannot handle as much back-pressures as the older engines do. - This however does not mean that their engine brake is weaker. If anything the opposite is true, as a higher compression makes for more resistance during jake operations.

As far as what is "safe" .. different engines have different upper-end ratings on this. Like others have pointed out, CM870's typically cap at about 28 psi, CM871's, a bit less that that, and newer CM2350's etc... its even slightly less. For most people ... if their engine brake programming has not been played with ... They should not normally have to keep an eye on their jake boost pressures while going down a hill unless they suspect something is wrong.

Jerry did the tune when they did the inframe. It has been doing very well since the inframe. I have been running really hard, infact I've got just over 30000 miles on it already. Jerry said he can adjust the tune if needed when I bring it back around 50000 miles. I haven't let it go to see how high it goes because I don't want to mess anything up. I didn't want to tear up an engine needing rebuilding I surely don't want to tear up a new inframe.

[Chamberpains]

Well you can have faith it was built to the highest standards. Hopefully you're running up above 1500 on a pull so you should have no fears of letting the jakes run in the same rpm range. If 18 psi is all you're getting out of it it is definitely low. Run the insite on/off test and look for full operating range of the actuator and check for air leaks in the actuator air supply. You still haven't mentioned what the psi is under a hard pull.

Read this http://rawze.com/forums/showthread.php?t...3#pid13433 for a bit of insight on the operating range we prefer and an isx should be used in.

[Ricky]

(06-05-2021 )Chamberpains Wrote:  Well you can have faith it was built to the highest standards. Hopefully you're running up above 1500 on a pull so you should have no fears of letting the jakes run in the same rpm range. If 18 psi is all you're getting out of it it is definitely low. Run the insite on/off test and look for full operating range of the actuator and check for air leaks in the actuator air supply. You still haven't mentioned what the psi is under a hard pull.

Read this http://rawze.com/forums/showthread.php?t...3#pid13433 for a bit of insight on the operating range we prefer and an isx should be used in.

It wants to go over 20 but I just don't let it because I thought 20 was a high. I have heard people talk about dropping valves so I was playing it safe. I truly trust the build, I was there and saw Alison's attention to detail. Plus everything from the head up is new except the injectors and they tested good. I have been around trucks and shops most of my life, I really liked Jerry's crew. They worked together good and do it right and they truly care and it shows. As far as keeping the RPMS up, I do. It's tough sometimes since I have the Ultrashift transmission but I like it because my left knee is messed up. I keep the RPMs up climbing hills by slowly down.

[Chamberpains]

Dropping a valve only happens in extreme cases. There has to be something seriously wrong with the engine. Like weak worn out valve springs, the engine mechanical timing is wrong, worn out valve seats, faulty valve (usually manufacturers flaw) or maybe if you would happen to run the jakes on full blast with the rpm's screaming up above its rated rpm range but even then I have my doubts that in limited uses up there it would actually drop a valve. These engines are that well designed.

You have an incredibly designed engine from Cummins that was hand built by the best team in the country to build one using only the best parts available. You can have faith that if you keep good clean oil in it and operate it within the ranges rawze describes then you will be able to do very little to that engine to hurt it. That is what the programming geniuses from Cummins have done. They spent millions of $$ on R&D to find the safe limitations of things and put those limits in the ECM. If it's demandated and you completely trust the person that did it then you will also know they haven't severely altered anything as to allow the engine to operate outside those safe ranges.

I drove my demandated cm870 exactly how rawze describes and how I described for 300,000 miles till my stupid neglect of not changing main bearings at a million miles allowed the engine to lose #5 piston wrist pin at 1.1 million miles. I replaced the engine and continued to drive the new reman for 250,000 more miles in the exact same manner. It still fires up today and runs just as good. I never once dropped a valve or had any ill effects running my jakes in the manner I described. Even in my whoopsy doo moments of grabbing a gear too early the rpm's screamed up to 2100-2200 for a second and still no ill effect. And that was in an engine with over 1 million miles.

These are incredibly built engines. The jakes on your engine will easily handle the ranges I described. It absolutely will save you a pile of money on brake replacement. Let them do what they are designed to do. And if all you're seeing out if your cm870 is low 20's or below psi when your on a hard downgrade fully loaded with the rpms up in the 1600-1850 range and down a gear or 2 off the top gear (top gear would operate at 25-28 max) then you're not getting full jake out of that engine. Hard high jaking will easily produce 28 psi if not slide up in to the 30-32 psi range (when in really extreme hard jaking) don't be afraid to allow it to go there.