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.

[Magard]

Hey gearhead, I the spirit of understanding. Can you tell me if the boost pressure is measured at the intake manifold by a manual gauge wouldn't that indicate how much charge flow can enter the cylinder through the head. Smaller ducting to the intake manifold should equal more velocity less time to cool in charge cooler but same charge volume just less dense because it is warmer. Anyhow you can probably tell I'm in a Volvo. When I seen that air compressor snorkel I thought that was more restrictive than anything else in the system.

[gearhead]

(02-03-2017 )Rawze Wrote:  

(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.

I am not disagreeing that it is to much boost i said that it was to high. I only stated why it is damaging. The reason is cylinder pressure. I am agreeing just trying to explain why it is a issue.

[gearhead]

(02-03-2017 )Magard Wrote:  Hey gearhead, I the spirit of understanding. Can you tell me if the boost pressure is measured at the intake manifold by a manual gauge wouldn't that indicate how much charge flow can enter the cylinder through the head. Smaller ducting to the intake manifold should equal more velocity less time to cool in charge cooler but same charge volume just less dense because it is warmer. Anyhow you can probably tell I'm in a Volvo. When I seen that air compressor snorkel I thought that was more restrictive than anything else in the system.

Chargeflow is calculated based off of several things one is boost others are things like turbo speed,egr delta pressure,exhaust backpressure. It is a measure of volume of air so yes smaller piping will reduce volume. Think in terms of a hose, lets say that i have a 1 inch hose and i am pushing water threw that hose at 20psi. Now take anouther hose at 3/4 inch and pump at 20psi you will not get the same amount of water. So increase the pressure of the 3/4 hose to 30psi and you might get the same amount as the 1 inch hose. Now let me stop and explain i have in no way said that these figures are correct i have not done the math LOL. Just an example. But in terms of your engine you would be way better off in some ways to be with the 1 inch hose. The psi is lower but yet you get the same volume of air. This reduces backpressure on the engine because of the ratio law with turbos. Lets say your turbo for argument sake has a 1 to 1 ratio which is dam good under full boost. With that being said if you make 1psi of boost you would make 1 psi of backpressure between the exhaust output and the turbo. With the vgt on the cm2250 and the cm2350 the ratio is more like 4 to 1 at full boost. So now we have an even bigger problem with things because the more boost you build the more backpressure you build.
So that's part of the reason for running less boost. I have learned that when you try to push the turbo at 40psi you are making so much backpressure that you are literally working backwards. The more you try to push it the exhaust cannot get through the turbo. So your fuel mileage will suffer from this. It's like a giant balancing act with making the motor last as long as possible. Keeping the backpressure low and cylinder pressure to a minimum will make the head gasket and liners in better shape. I do not wish to disagree because rawze in fact is correct. I only try to explain what i have seen and to help everyone to understand why the high boost can be a problem on a higher compression engine like the common rail cummins. I have a hard time putting my thoughts into writing so sometimes i word things in a weird manner and sometimes i will type something in a manner that looks different from what i ment to say if that makes any since.

[Magard]

I can understand the hose analogy. I also appreciate the turbo back pressure discussion. I always wondered how much back pressure it took to create boost. When I seen how restricted the inlet of the intake manifold was I couldn't believe that Cummings did that. I wonder if anyone has checked the pressure difference before the manifold compared to in the manifold. Combine that with a small charge system and it has to really make the engine work, just to breath. I was just thinking of once the air was in the manifold at a certain psi all it had to do was get into the cylinder through the head. But with all this back pressure difference it would throw off actual charge volume due to valve overlap. (I'm guessing there's valve overlap.) Hey thanks for the time. I just like to know what my machine has to do when I ask it to do it. Back pressure to drive turbo is something not thought of much unless your really on your game with custom tuning. Awesome.

[zare6]

Hi gentlemen, I want to bring this back on track. The boost may be high and has always been 38 psi right from new and the fuel mileage was 7mpg nothing has changed but the mileage on the truck. The egr the dpf all the emissions have been checked and or cleaned. So here we are 200000 miles 38psi boost pulls like a freight train but 5 mpg. I decided to do a custom tune, the boost went to 43psi pulls incredible fuel mileage is now 4.5 mpg.

[mmssvv]

(02-04-2017 )gearhead Wrote:  

(02-03-2017 )Magard Wrote:  Hey gearhead, I the spirit of understanding. Can you tell me if the boost pressure is measured at the intake manifold by a manual gauge wouldn't that indicate how much charge flow can enter the cylinder through the head. Smaller ducting to the intake manifold should equal more velocity less time to cool in charge cooler but same charge volume just less dense because it is warmer. Anyhow you can probably tell I'm in a Volvo. When I seen that air compressor snorkel I thought that was more restrictive than anything else in the system.

Chargeflow is calculated based off of several things one is boost others are things like turbo speed,egr delta pressure,exhaust backpressure. It is a measure of volume of air so yes smaller piping will reduce volume. Think in terms of a hose, lets say that i have a 1 inch hose and i am pushing water threw that hose at 20psi. Now take anouther hose at 3/4 inch and pump at 20psi you will not get the same amount of water. So increase the pressure of the 3/4 hose to 30psi and you might get the same amount as the 1 inch hose. Now let me stop and explain i have in no way said that these figures are correct i have not done the math LOL. Just an example. But in terms of your engine you would be way better off in some ways to be with the 1 inch hose. The psi is lower but yet you get the same volume of air. This reduces backpressure on the engine because of the ratio law with turbos. Lets say your turbo for argument sake has a 1 to 1 ratio which is dam good under full boost. With that being said if you make 1psi of boost you would make 1 psi of backpressure between the exhaust output and the turbo. With the vgt on the cm2250 and the cm2350 the ratio is more like 4 to 1 at full boost. So now we have an even bigger problem with things because the more boost you build the more backpressure you build.
So that's part of the reason for running less boost. I have learned that when you try to push the turbo at 40psi you are making so much backpressure that you are literally working backwards. The more you try to push it the exhaust cannot get through the turbo. So your fuel mileage will suffer from this. It's like a giant balancing act with making the motor last as long as possible. Keeping the backpressure low and cylinder pressure to a minimum will make the head gasket and liners in better shape. I do not wish to disagree because rawze in fact is correct. I only try to explain what i have seen and to help everyone to understand why the high boost can be a problem on a higher compression engine like the common rail cummins. I have a hard time putting my thoughts into writing so sometimes i word things in a weird manner and sometimes i will type something in a manner that looks different from what i ment to say if that makes any since.

Interesting!
On my cm2350 ratio exhaust to boost never come more then 2:1.Wondering now, is this ok.Boost at full throttle 32psi,turbo speed around 110k

[gearhead]

Only because you are at 32 psi and the ratio changes the higher the boost levels. I have seen 1 to 1 on cm871 until about 16psi or so. You can check your ratio by monitoring your gauge exhaust backpressure against you boost pressure gauge. Gauge means that barometric pressure is not added to the value. If you use insite to monitor it you have to subtract about 15 from value to get gauge number. You can tell because it reads the same as your barometric pressure sensor with the key on and truck not running.

[Unilevers]

(02-04-2017 )zare6 Wrote:  Hi gentlemen, I want to bring this back on track. The boost may be high and has always been 38 psi right from new and the fuel mileage was 7mpg nothing has changed but the mileage on the truck. The egr the dpf all the emissions have been checked and or cleaned. So here we are 200000 miles 38psi boost pulls like a freight train but 5 mpg. I decided to do a custom tune, the boost went to 43psi pulls incredible fuel mileage is now 4.5 mpg.

43 psi?!? who did that you need to take it back there and tell em to turn the dam boost down! you are going to grenade your head in very short order.

i dont think i did but if i did get ahold of me asap so we can get that sorted out. if i didnt get it sorted out anyways!