Rpm range?

[Rawze]

(03-13-2017 )Rockycoon75 Wrote:  I have been searching and have seen several answers. What is the correct RPM range to run a bone stock 871 in. Trying to learn more about these and trying to get better mileage. Truck has 485/1850. 18spd 3.55. I have been told to lug to 1200. Then told to keep above 1450. Don't want to destroy it from ignorance. Thanks

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This bullS$it maximum 1500 rpm or less crap I see over and over...

The ISX 15-litre engines have no problem handling up to 2400 RPM, and i have seen them run at 2700 RPM under competition in the past. 1700, 1800, 1900, or even 2100 RPM is no problem for them at all. Being scared and only running them below 1500 and never going above this is complete and utter bulls$it that comes from the student-mill mega-fleets brainwashing, their governed trucks, and their abusive drivers who like to tear s&it like drive-trians and trannys up when they are allowed to use higher rpm's. - It has nothing to do with engine longevity, believe me they could care less about that.

The main working rpm range = 1100 - 2100. A difference of 1000 RPM. Driving it no more than 1500 all the time is driving it in only its bottom 40% of its working range. Think about that for a moment and realize how ridiculous that is.

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Everyone so far has given some good things they do so I will take a different approach to answering this question. i will base my answer solely on what I have seen happens to the insides of the ISX based on how they have been driven, I don't care about anything else or how someone else treats their trucks...

I also don't give a damn WHAT the engine maker, or the salesman, or anyone else says on this subject who has not re-built a bunch of them, then compared the results to how they were driven. This also means, no offense, but I don't give a damn what ANY driver says who has not re-built their own ISX engines a few times themselves. - I see how people tear them up with abuse and too much power and all the other things that got them there.


That being understood, this is what I have to say based on what I have seen ...

First and foremost, When you need maximum torque and power, because that always seems to be the biggest question ...

The guys down under in Aussie land, who load ISX engines up with 80-90% torque load for hours and hours and hours on end with their road trains, abusing the complete snot out of them way worse than anything I have seen in the states, all eventually say the same thing to me. They say an ISX will hold up the longest at 1650 RPM under those kinds of conditions. Lower RM ranges, you can forget about it. They will not hold up very long under about 1500 or so, and almost always have liner/head issues. This is why they gear almost always the trucks for 1650 specifically.

Still referring to only max engine loads here, next is the fact that the lower RPM you drive one in, the more internal vibration to the liners on ANY diesel engine, i don't care what make and model it is. This becomes especially prevalent below about 1300 RPM or so and can be downright damaging below about 1200 on an ISX. I don't care what model (870, 871, 2250, 2350) you have... OR WHAT THEY ARE ADVERTISED AT!>

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These things tell me very clearly that the more power and torque you demand from one, the higher rpm range it should be in. This would be up to about 1700 or so, 1900 being the high end. Remember, 2100 is roughly its upper end, not some bulls$it 1500. This equates to down-shifting early when you know you are going to need lots of power and bringing the RPM up to 1600-1900 , then shifting again when it gets to 1500, back up to 1800+ again,.. such and so fourth. This would produce the least amount of internal vibration and wear in the engine under heavy loads and keeps the air moving through it.


ON THE OTHER HAND...

The engine's rpm range for best fuel efficiency is always changing based on load demand. When heavy, it is the HIGHER rpm ranges that give the best efficiency actually, and when not under any load, that is the only time that the lower rpm makes a slight difference. No load at all on the engine (10% or less), below 1300 rpm will be the most fuel efficient, and at heavy (70%+), 1700+ is more fuel efficient. It is a curve based on what is being done. There is no set place for optimum rpm vs fuel efficiency at all on these engines. it is always changing based on what is being done.

SO...

The answer is NOT WHAT RPM IS BEST,... but --- WHAT RPM AT WHAT LOADS YOU ARE CARRYING...

Bobtail, least rpm you can get away with .. Light loads, 1200-1400 rpm is good for cruising, higher rpm's when you get into a hill. .. Heavy loads higher RPM all the time, above 1400 and down a gear unless someone is on flat ground. .. Really heavy loads, 80+above, keep that thing wound up and in the high rpm range all damn day. It will run better in the 1500 - 1900 range and even average better efficiency in most terrain too.

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Take all this with a grain of salt, it is not any kind of final authority or anything, it is just my own findings based on what I have seen myself. This is also how we choose to drive our own truck, but I can tell you that we use a variation of RPM ranges based on demand but we also typically DON'T PUSH THE PEDAL DOWN MORE THAN 1/3 EVEN ON THE STEEPEST GRADES OUT THERE. WE DON'T USE HIGH AMOUNTS OF POWER AND TORQUE. We baby the hell out of our truck 100% of the time because fuel mileage and longevity are more important to us than anything else we do. We choose to keep our boost below 15-lbs or so and use lower gearing instead. Even then though, on a steep grade, we keep it at 1500-1700 during the pull.

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rpm, engine rpm, isx rpm, best rpm, best isx rpm, isx optimum rpm