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Discussion Starter #1
I have been following the ISV since DieselPower had the article about the Cummins V6 and V8 programs and some rendered images were released. The head design reminded me of existing 32 valve V8 Turbo diesels, complicated.

As more details about the ISV came to light and it started to trickle out to the OEM manufactures for commercial applications I released this was an innovative engine. Perhaps the most advanced turbo diesel V8 engine currently available.

The key points that stood out to me were:

-Displacement
-Bore and Stroke
-Head Design
-Turbocharger selection

Displacement

Displacement is a crucial factor, it sets the inital mass airflow possible through the engine. To me 5.0L is about the right displacement for a gasoline V8, not too much rotating mass but enough displacement to move most loads without much effort. With a turbo diesel until the turbos spool up you have to rely on displacement alone to get going. The additional two liters of displacement over the ecodiesel 3.0L is going to mean the Titan XD will outclass the Dodge for towing and raw performance.

Bore and Stroke

I find the bore and stroke really interesting, a bore of 94mm and a stroke of 90mm. Traditionally diesel engines had a stroke that was longer than the diameter of the bore. The 5.9L for example has a bore of 102mm and a stroke of 120mm. Older diesel engines needed longer strokes, because lower injection pressures meant it took longer for all of the fuel to fully vaporize. Most engine manufactures have not changed their mindsets to address the fact of high pressure common rail injection with multiple injections per combustion event. What this means is that the diesel can be fully and cleanly burned in a shorter stroke. So by going to a bore that is greater than the stroke, for a given displacement that means the piston has a greater surface area exposed to combustion gases. Even in gasoline engines a longer stroke increases the available torque, but at the expense of peak RPM.

Head Design

From the available images released from Cummins, the head design of the ISV appears to have plenty of input from Nissan. While there are other dual over head cam diesel engines out there, the valves are not parallel to the cam shafts which complicates the valve train design. The valves on the ISV appear to be parallel with the cam shafts which simplifies the rockers and the heads.

For a time a big deal was made about the 6.7L Powerstroke and the 4.5L Duramax engines having the exhaust ports on the inside of the valley. I originally thought that was a good idea and I was a little bit surprised Cummins did not choose to follow that route. This is another place where Nissans involvement seems to be apparent. Nissan has always been very thoughtful about tuning intake and exhaust runner lengths, the ISV, like the Nissan VH45, has siemesed intake ports and tuned intake runner lengths. The head and intake design of the ISV closely resemble the design of the VH45DE. A key notable difference is that the ISV has only one chain drive sprocket and a gear drive for the exhaust cam whereas the VH45 has a chain sprocket on each cam. The tall intake manifold with tuned length runners leaves plenty of room for the turbochargers.

Turbocharger selection

The choice of using compound turbos for the Titan shows Cummins and Nissans intention to have a high performance diesel engine in the Titan. Compound turbos provide excellent response, efficiency and scalability. Due to the nature of compound turbos, a small increase in pressure ratio on each turbo works out to be a rather large increase of final pressure ratio. As an example, a single turbocharger with a pressure ratio of 3:1 will produce around 29lbs of boost. Changing the pressure ratio to 3.5:1 will make about 36lbs of boost. In a compound setup, the turbochargers can be aligned to their ideal pressure ratio, mass flow to work within the highest efficiency island. So compound turbos, each at a pressure ratio of 2.5:1, create a final working pressure ratio of 5.25:1 or close to 76lbs of boost. So from the aftermarket standpoint, if each turbo was increased to a pressure ratio of 2.6:1, a modest increase would barely effect the efficiency of each turbo. This small change would net ~83psig of boost.

The maths, if you're curious:

Atmospheric pressure multiplied by low pressure turbo pressure ratio multiplied by high pressure turbo pressure ratio minus atmospheric pressure. It's not quite that simple as the density of the gas is reduced as the temperature of the gas goes up. Compressing the air heats it up, thus the need for intercoolers.

Conclusion:

Using dual over head cams, compound turbos with an over square bore and stroke the ISV is destined to be the most advanced and high performance diesel engine available in a pickup truck. I'm looking forward to seeing the Titan in person. I truly hope that I will be in the position to be one of the first to order the new Titan.
 

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Thanks for this.
Didn't realize they had shortened the stroke so much.
Very different from other diesels.

And that Holset Turbo should prove nice too.

Here's hoping it all comes together for this Cummins in the Titan XD.
 

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...
Turbocharger selection

The choice of using compound turbos for the Titan shows Cummins and Nissans intention to have a high performance diesel engine in the Titan. Compound turbos provide excellent response, efficiency and scalability. Due to the nature of compound turbos, a small increase in pressure ratio on each turbo works out to be a rather large increase of final pressure ratio. As an example, a single turbocharger with a pressure ratio of 3:1 will produce around 29lbs of boost. Changing the pressure ratio to 3.5:1 will make about 36lbs of boost. In a compound setup, the turbochargers can be aligned to their ideal pressure ratio, mass flow to work within the highest efficiency island. So compound turbos, each at a pressure ratio of 2.5:1, create a final working pressure ratio of 5.25:1 or close to 76lbs of boost. So from the aftermarket standpoint, if each turbo was increased to a pressure ratio of 2.6:1, a modest increase would barely effect the efficiency of each turbo. This small change would net ~83psig of boost.
...
Frankly, I know little about turbos, but it sounds like you're describing a sequential turbo setup.

It's my understanding that the M2 Holset uses the bypass valve to adjust the amount of exhaust gases to the two turbos in a parallel fashion. Here's a quote from a Holset brochure I downloaded:
At low engine speeds, the rotary valve is positioned so that
all the exhaust gas passes through the small turbine. The gas
passes through the second, larger turbine afterwards, but as the
flow is small and the second turbine is big, only a small amount
of energy is extracted here. As engine air flow increases with
engine speed and load, the electrically actuated rotary valve
modulates to allow an increasing amount of exhaust gas to go
directly to the large turbine. This large turbine increases its work
contribution whilst the work done by the smaller turbo stays
relatively constant. At high engine speeds, the rotary valve diverts
most of the exhaust gas directly to the large turbine, leaving the
small turbo contributing very little.
In this condition, the compressor bypass valve is opened to
avoid the small compressor becoming a restriction to the
incoming air. At this point the system is now working as a high
flow single-stage turbocharger.
 

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2019 Titan XD Pro4x Cummins
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Discussion Starter #4
It's a compound/sequential arrangement. Runs as compound until the low pressure turbo can handle the whole load.

You'll notice that any exhaust gas exiting the high pressure turbo is directed to the turbine of the low pressure turbo.
 

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Cant wait to see what Banks does to this motor. and of course EFI.

I really cant wait to take one for a test drive. I never wanted to have another truck loan but this truck might persuade me otherwise. Also means i can buy a bigger trailer, tractor for work, and of course a nice toy hauler. which also means i gotta buy a dirtbike again and a side by side.
 

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EXCELLENT piece Navy, Cheers. I wasn't aware this much technical information was available yet...

Question to all, how much do you think we need to worry about Turbo longevity if small tweaks net those massive gains in boost? I'm thinking once guys like Banks et all start tuning them. (I'm not saying they don;t know what they're doing and will grenade the thing, just genuinely curious what people think the threshold is?)
 

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The Holset M2 Turbo is brand new for this Titan XD 5L Cummins.
AFAIK It wan't used on the earlier ISV 5Ls in school buses and so on.
So nobody really knows how dependable it is.
Cummins and Holset have a good rep though, so there shouldn't be any issues.

But when people start tuning ... anything is possible and lots can go wrong.
 

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Now that has me feeling a little uneasy about it. Might be one of those times that sitting on the sidelines and seeing how initial trucks do.
 

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Nah. It should be good. Besides turbos are rarely a problem with modern diesels. It's usually the emissions or the Bosch 4.2 fuel pump. And even there, they seem to have gotten things under control recently.

But I would wait on tuning anything until the tuners have proven they won't blow up your engine.

And yes, I won't be lining up to order a brand new truck. But maybe next year?
 

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2019 Titan XD Pro4x Cummins
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Discussion Starter #10
Turbochargers are very simple. It appears both the low and high pressure turbos are fixed geometry which are very simple and reliable. The rotary valve is very simple in design but is the only weak link that I can see.

Compound setups are easier on the turbochargers, so they could be turned up well past what the injectors can feed before getting too far out of their efficency islands.
 

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Cummins Columbus Engine Plant: Home of the 5.0L V8 Turbo Diesel


"Here is a sneak peek of the heritage and hard work that went into creating the all-new Cummins 5.0L V8 Turbo Diesel that will deliver all 555 lb-ft of torque to the 2016 Nissan TITAN XD"
 
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