ISX 2350 485

[gearhead]

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.