Cm870 upgrades

[Marajin]

(01-27-2017 )Running rough Wrote:  my 870 well now 871 will have a slight uneven ideal that is barley noticable, i would not call it a miss and more like slight uneven fueling between cylinders and same thing it has idealed like that ever since i can remember, i have seen numarous 870 and 871s in my area and guess what they all pretty much had that same ever so slight unevenness when sitting and idealing, my opinion is this if it is not bad like a 25 rpm flucutation then there is probly notting wrong, i have changed actuaters all new injecters, presure relive valves in search of that perfact ideal, the 871 870 with concept gears at operating temp is a quieter moter then my 2250 but the 2250 cpl3606 ideals 100 even and sounds more like a cat,i think its the nature of the desighn of the fuel system on the 871 870, feeding 6 injecters with 2 timing and 2 metering syliniods, if one of those timing actuaters sticks even slighty you will hear it on the ideal, it is kind of of funny though that with the mandate intact they same to ideal evener, it could be the backpresure on the engine, i am thinking, one thing is for sure the single overhead cam commen rail isx does have a more even ideal, from my experience anyways, but i still like those older ones to

Stock program loads engine up with 8 hp roughly of internal engine load via over-boosting the turbo at idle. It also makes engine warm up quicker and have less valve lash when its cold. Any time you place a slight engine load on a big engine, they will idle slightly smoother and have less lash. MM can be set any way you like, but generally most people want to save fuel at idle as much as possible. Remove this internal loading and factory over-boosting makes the fuel consumption go from about 40 mg/stroke down to about 15. This is certainly a big jump in fuel savings at idle!. But the engine also sounds different, takes longer to warm up, and has more lash especially when cold because of it.

Letting the engine "free-float" with little to no load or only slight positive pressure on it will also make it much more sensitive to a weak fuel component and it may even reveal problems that the higher fuel consumption or internal load may have been masking. I have seen this before with worn out actuators, leaky injectors and such, and you guess it. - Sometimes when this happens the engine will run rougher as a result and the truck owner will complain that the stock program made it run smoother. Some tweaking to MM can put it back, and make it suck the 40 mg/stroke again and mask the rougher idle, worn out actuators, etc. - OR someone can take the time to find the issue and solve it properly.

Because I am on this subject -> Another thing that I think gets overlooked is the piston rings. Taking away all that positive pressure on a worn out engine will make worn out piston rings float around more in their seat at idle as they become less carbon packed after a de-mandate. This will make for increased blow-by and higher oil consumption. I have seen some engine that had a million on them already with stock mandate and programming get these changes go from no oil consumption to suddenly start using a gallon of oil every 2000 miles. - You know damn well the rings were already worn out, but all the carbon packing and extra positive pressure was masking it the whole time. Putting the boost pressure back into it at idle will make it slow down again, but even there as well, it is better to do the right thing and fix the engine instead. - I seen have piston rings that get so thin from masked blow-by, carbon packing, and sooted up engines that it is a wonder they didn't break and destroy a cylinder.

Just because an egr engine don't have much blow-by doesn't mean the liners and rings are not completely worn out. I have seen it plenty.

+++++

It think is all a preference to what most people want of choice. A lot of people don't want to waste fuel at idle just because it makes their engine sound a bit smoother, and it definitely does not hurt anything to let it "free-float". A trade-off of quite a bit of Less fuel used? - or consume more fuel to make it sound smoother and warm up quicker at idle?- Your choice but either way it does not cause any long term issues. If anything, a slightly sloppy valve train at idle has been shown to help keep oil flowing nicely on the top end to all the rockers, crossheads, cams, etc. The little bit of lash that you hear in the rockers also keeps them from getting clogged up with deposits from what I have seen too.

An easily noticeable rough idle or running on the other hand is not so good for any engine. It stresses the components in unusual ways and can be harmful under engine load. Solving that as much as you can is always important so if your idle is set for as little boost as possible and engine is "free-floating" using a lot less fuel, then it is important to make sure all your injectors and actuators are in good shape too.

[Rig Wrench]

(01-27-2017 )Running rough Wrote:  

(01-26-2017 )Rig Wrench Wrote:  Well, its alive. Just got to do some finishing touches to it. Sounds good. Everything seems in check. One question i have though, is when it is first started, it seems very rough, rpms fluctuate back and forth quite a bit, it levels off after it warms a bit. It has done this ever since I can remember, I feel like the 3 other cm870s did the same thing. Anyone else run into this?
Thanks again for the input and kind words
What it started out

just curius how many hours or miles you had on it and what justified a rebuild, what shape were the liner seats in, did you have to cut them

Liner seats didnt look bad. Cut em to .014 just as a precaution. It has right around 850 on it. But also get 3 hours minimum pto time everyday as well. Cant recall exact hours. We rebuilt cause front cover was leaking bad, was starting to use a little bit if coolant, and the owner had a spare truck at the moment

[Lostfarmboy]

Rawze Wrote:Grinding out the outlet port on the cold side of the turbo and polishing it does make for slight gains. Polishing the 90 degree elbow that attaches to it does too. This is true for any model Holset I have seen. The rough cast has its place in creating a wall-flow barrier, and improving flow, but the joint is just not quite big enough, and the bend just steep enough at higher flow rates, causing the effect to become unstable. Polishing out the rough surfaces to a high degree (close to mirror finish) proves to have a better effect in every case I have seen it done, including my own truck when I tried it. - Mine gained almost 0.3 mpg. Very difficult to get gains out of a truck that is already breaking 8+ all the time, so it definitely worked.

Rawze, I for one would be very interested in hearing more about how you did this and what you used to do it.

[Rawze]

(09-08-2019 )Lostfarmboy Wrote:  

Rawze Wrote:Grinding out the outlet port on the cold side of the turbo and polishing it does make for slight gains. Polishing the 90 degree elbow that attaches to it does too. This is true for any model Holset I have seen. The rough cast has its place in creating a wall-flow barrier, and improving flow, but the joint is just not quite big enough, and the bend just steep enough at higher flow rates, causing the effect to become unstable. Polishing out the rough surfaces to a high degree (close to mirror finish) proves to have a better effect in every case I have seen it done, including my own truck when I tried it. - Mine gained almost 0.3 mpg. Very difficult to get gains out of a truck that is already breaking 8+ all the time, so it definitely worked.

Rawze, I for one would be very interested in hearing more about how you did this and what you used to do it.

a dremel tool and a few hours of patience. My cold side outlet port was so bad, it actually had a flat spot and a hump in the cast when I started. I removed them and did them off the turbo.

[Lostfarmboy]

Sounds like I have a new project