ISX 2350 485

[gearhead]

To much boost and too much backpressure. Your loosing your mileage from the backpressure.

[mmssvv]

(02-04-2017 )gearhead Wrote:  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.

This is true.Then at 32psi boost ,I have close to 50psi exhaust,just checked my data.This mean the ratio is about 1:1.56 which sounds right for my turbo.
Thanks!

[Magard]

Would a small or large vg turbo have a better back pressure ratio at say 35 psi. I would think the small turbo would be better because the hot side would be open more and the cold side needs more rpm to create volume but I'm just guessing. Kinda like a lower gear because the turbin isn't as big.

[gearhead]

There is alot more to it than just size. The ar ratio of the housing. In cm2250 the turbo is alot smaller overall to make it easy to spoll. One of the main reasons for the vgt is a way to control backpressure for the egr valve. Cummins made a motor in Australia cm2250 only has scr system no dpf and no egr. It has a non vgt hx60 just like the pre egr cm570. I really don't think cummins was thinking about the vgt for the sole purpose of fuel mileage. If that was the case the the cm2250 from Australia would also have vgt. I can't speak for them this is just my opinion. But the truth about the vgt being a way to control back pressure is definitely true. They needed a way to close exhaust off some to make the exhaust go through the egr valve.

[Logger]

My 2350 600,since new has made 38psi boost. Has 60k on it now. For that engine is 38 to high also?

[schISM]

(02-05-2017 )gearhead Wrote:  There is alot more to it than just size. The ar ratio of the housing. In cm2250 the turbo is alot smaller overall to make it easy to spoll. One of the main reasons for the vgt is a way to control backpressure for the egr valve. Cummins made a motor in Australia cm2250 only has scr system no dpf and no egr. It has a non vgt hx60 just like the pre egr cm570. I really don't think cummins was thinking about the vgt for the sole purpose of fuel mileage. If that was the case the the cm2250 from Australia would also have vgt. I can't speak for them this is just my opinion. But the truth about the vgt being a way to control back pressure is definitely true. They needed a way to close exhaust off some to make the exhaust go through the egr valve.

I know, I know this is gonna flare up the "fixed" vs. "variable" vane turbo squabble again but I'm gonna say Cummins wasn't thinking about fuel mileage at all with the VGT, only a means to regulate the pressure differential of drive/compressor pressures in order to introduce egr into the intake in the amounts they were looking for.
Not only the Australian ISXe5 but also the new European QSM 12 liter and the smaller 3.8 through 9 liter tier V emissions engines introduced this past year don't have egr. Cummins could have used the VGT turbo on these engines but chose not to.
I'd say that's a pretty good testament to the efficiency that can be had by a fixed vane turbo that maintains a correct a/f ratio without relying on a pre-plotted table that might be just a little off in certain situations. Just my .02 cents.

[gearhead]

Wasn't going there just stating pure facts that's all.

[Rawze]

You guys can keep spewing your ideas all you want to but someone has to be pretty dumb to think a fixed turbo is across the board going to be more efficient than one that is programmable and adjustable (variable geometry) on any engine that has to adjust to a wide variance of torque, speed, and RPM ranges on a constant basis.

First of all, those engines still have heavy emissions controls through the combustion process, VG, EGR valve, external EGR piping or not.

No one has considered that with no need for external EGR piping, it is simply cheaper and more profitable to stick a non-vg on the engine when they sell it. More profit for the engine maker and slightly higher reliability would easily be my first conclusion. Has nothing much whatsoever to do with making the engine "more efficient" by not staying with a VG. - It is simply a matter of cost difference vs how close they maintain efficiency in its same class.

YOUR PARTICULAR APPLICATION is what comes into play most of all on how an engine (and truck) should spec'd and what will be the most efficient combination of components will be for you. It is as simple as that. For most trucks here in the states, there is too much variance in what they do for a non-vg to even come close in most applications. For the few that have a constant high-torque application it still does not really "beat" a VG by any stretch of measurable means to make up for the costs of conversion from one to the other. They never get their money back on the investment made because the long term gains are just not there.

[Hermjeji]

CM2350, ISX15 550, 2015

Boost pressure measured several times, EGR tuneup completed, goes up to 38PSI. ECM was flashed with latest calibration a few years ago. This is from the factory sensor and not a secondary boost gauge. The truck is due for DPF bake and de-ash. However, i was looking at some data I collected a while ago when the truck was pulling some short 5-10% grades loaded in the city, what is the max turbo speed supposed to be? This one is getting above 100,000 RPM.

Also - did the overhead set a few weeks ago, same results afterwards. No axial turbo play, impellers looked good on the intake side.