ISX 2350 485

[Rawze]

(02-03-2017 )gearhead Wrote:  A lot of these engines came this way stock nothing you can change parts wise will change your boost. If you want it to go lower it will require custom tuning for sure trust me i know.Your truck is not the first. This is very common 80% of cm2350 and cm2250 push 38psi. It all boils down to the end result cylinder pressure which cannot be measured on this engine definitively. With that being said charge flow is more important than psi but they both effect the end result. which is cylinder pressure. Lets say you have 100lbs per minute at 40psi with one turbo and with another turbo you can have 100lbs per minute at 35psi same thing at the end of the day with cylinder pressure it is all about the volume of air not pressure this is why cummins uses this method of charge flow control. What is being stated is that 38psi is to much volume for that engine with higher compression ratio.
although cylinder pressure can be controlled with injection timing. The bottom line is the only way that your boost is going to drop is by custom tuning period. The ecm is doing what it was told to do. The motor will last longer by dropping boost down to about 34 to 35.

I figured this would turn into a debate, that is great. Everyone learns from it, including myself.

From the 2350 trucks I have helped others that were NOT de-mandated or custom tuned, etc. It has been about 20 or so. They all seemed to want to peak about 32-33 from factory. I only have occasionally come across one that would get up to 38 (maybe only 1 or 2). Perhaps my experiences just happen to be a bit deferent than from what you have seen.

What was not mentioned here so far is that through well established custom tuning methods, is that testing, dyno, fuel mileage records, etc. -- They all show clearly that 38-lbs boost is a bit too much for that model engine even at that higher factory HP settings.

Combine these two bits of info together and I would tend to think 38 is not normal for one. That is why I said what I did. it has merit, but it does not mean it is the only answer by any means.

- Maybe some of the factory programs are set too high and over-boost for emissions reasons?

I would not doubt that they do whatever they can to make em pass the mandate specs above making them run better. I have had one person who's truck did make that much bopost report to me once that when they did tune-up work and got everything working really well, the boost levels actually went back down. This leads me to believe that is is not always normal for them, but like you say, some may actually be programmed that way from factory, or may have different mandate requirements that make them tend to boost that high.

Either case, it would be interesting to know for sure if it is a programming difference on some engines, which ones would cause it and which ones do not. Certainly 38 is high for one, considering its compression ratio and other specs.