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Great animation here, directly from Nissan!


The Cummins 5.0L V8 Turbo Diesel in the upcoming 2016 Nissan TITAN XD features a unique Cummins M²™ Two-Stage Turbocharger is configured to work well at both low and high engine speeds. The series sequential turbocharging system, involving two differently sized turbochargers, effectively provides a small turbocharger for low air flow requirements and a large turbo for high air flow.
 

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Compound Turbos are very cool. It appears to be a hybrid of compound and sequential, very cool.
 

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Does anyone knows if this type of turbo would increase engine efficiency in addition to reducing "turbo lag"? Is the "single" turbo essentially useless at low rpm, creating unnecessary load on the engine? Could this type of arrangement increase mpg in the city, when engine is at low rpm?
 

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What do they mean by "perceived lag time"? Seems to me that lag time exists or it doesn't. Perception doesn't really matter.
 

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Does anyone knows if this type of turbo would increase engine efficiency in addition to reducing "turbo lag"? Is the "single" turbo essentially useless at low rpm, creating unnecessary load on the engine? Could this type of arrangement increase mpg in the city, when engine is at low rpm?
If it is a true compound system, the efficiency is increased because both turbos can be designed to work together in their best efficiency islands. Compound turbos also have the benefit of extracting more work from the waste exhaust gas.

A compound turbo arrangement can reduce fuel consumption or increase it, depending on how you drive. Compounds allow for more air, better and cleaner burning, but the added power and response makes it easier to waste fuel in the name of fun.

What do they mean by "perceived lag time"? Seems to me that lag time exists or it doesn't. Perception doesn't really matter.
All turbocharged engines have lag, varying degrees of it. However using compound turbos and a six speed transmission, the perception of lag will be reduced. How? Sequential and Compound turbo setups spool up quickly and give you more available torque at lower RPMs. With the six speed the engine and tranny will spend less time hunting for the right gear, and instead rely on the engines torque and horsepower to do the job, with the sequential turbos spooling quickly.
 

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better and cleaner burning, but the added power and response makes it easier to waste fuel in the name of fun.
I agree with you here if someone wants to get that extra kick. If you don'tpress the accelerator to hard, don't use that extra power and response, fuel efficiencyshould go up. Otherwise you are absolutely correct on everything. That's whyaviation engines have multistage turbines-compressors combinations, whichrotates at different RPMs, to increase overall efficiency of the compressorsand therefore makes fuel burning more efficient.

Anyway, let’s hope that this turbo will help Titan MPG and bring it to somethinglike 21-26 (city-highway). :wink2:
 

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Isn't this essentially the same as BMW's Twin Scroll and Ford new Ecoboost?? Anyone know why Turbos are preferred for diesels and not say superchargers?
 

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The way I understand any pressurized air intake (havingcompressor in front of the cylinder air intake): it’s all about air-fuel ratio,better ratio=better efficiency=better engine volume to horse power ratio;smaller engine volume=better MPG. In simple words Ford Eco-boost smaller volumeengine have similar to non eco-boost payload with better MPG. Any “turbo” have a good efficiency at approximately50K rpm. At 5K rpm its efficiency drops to essentially 0. Having “turbo” whichcan operate at 5K to 50K rpm means wider range of engine rpms at which air-fuel ratiois in the sweet spot.
Forgive me if I am misunderstanding the “turbo”.
 

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In theory, if there was no friction and no parasitic losses, it would take the same amount of fuel for a 6.0L engine or a 1.5L engine to do an equal amount of work. However that isn't the case, so a 6.0L engine doing the job of a 1.5L is going to waste fuel because the engine is working outside of its efficency range.

A turbocharger is more like displacement on demand, so when you need the equivelent power of a 6.0L, you run a 4:1(3:1?) pressure ratio, forcing the same mass of air into the little engine.

Superchargers are not efficent, they are a major parasitic draw that is always there. Great for two-strokes and race engines, not great for flexability or efficency.
 

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Hope the actuator and linkage is well built, or the turbos will suffer like the Fords do with turbo issues...

The video looks like SolidWorks modeling ... Love that program ;)
 

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Nice video.
But nowhere did they mention "exhaust brake" :frown2:
 

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From Car and Driver regarding the Cummins Holset M2 Turbocharger

Now we’re talking about the Rotary Turbine Control, which is the marketers’ term for a single electrically controlled rotary valve that directs the exhaust flow to either of the two turbochargers or a wastegate depending on the engine load and rpm. At low engine speeds, the valve directs all of the exhaust gas through the smaller turbine. As airflow increases with engine speed and load, the valve rotates to favor the larger turbocharger, although some exhaust still spins the small, low-pressure turbo. To regulate the boost pressure, the rotary valve turns to open a path between the exhaust stream and the wastegate, venting waste gas around the turbines.

The rotary valve can also act as a throttle in the exhaust stream, raising the back pressure to act as an exhaust brake when the driver lifts off the accelerator. This throttle mode can also increase the work done in the cylinder, in turn elevating exhaust-gas temperatures to burn off the soot that’s been captured in the diesel particulate filter. The fact that this is all controlled by a single, rotating valve means that redirecting the exhaust stream can be done with smooth, supposedly seamless, transitions.
 

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Think that car&driver quote is from last fall, when Cummins first released more details about the 5L's dual turbo. ???

But since then, Nissan hasn't said a word about an Exhaust Brake, AFAIK. Maybe they think it's too technical, maybe it's built-in and operates automatically. Or maybe Nissan has decided to skip that functionality.

Sure would like to know one way or the other. Really odd that Nissan isn't talking about it as an Exhaust Brake is a major advantage of diesels. Especially when towing a 12K trailer.
 

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The design hasn't changed at all, so I am going to say that the quote is correct.
It is a feature of the new turbocharger, so why would they not use it.???
Maybe it isn't what you are looking for, but it is still an engine brake.
 

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I don't see an engine brake, and I doubt with the setup with this turbo would even allow one ...
 

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Cummins talks about the potential for an Exhaust Brake.
Nissan has not, so far.
If I were towing 12K, it would be nice to have.
Think we'll just have to wait and see.

Or maybe somebody can ask at one of the car shows where the XD is being displayed.
 

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About the Exhaust Brake, or lack thereof.

Apparently the big Ford diesels didn't have an on/off switch until 2015. Here's a description of how it used to work from another forum:
As for the engine brake, it works but you have to learn the trick of getting it to kick in. First the truck has to be in tow/haul mode. Then when you start down a hill you give the brake pedal a solid hard quick tap. Hopefully that engages the EB and if if does you'll feel it. You can then take your foot off the accelerator and coast down the hill at about the same speed that you engaged the EB at. I usually aim for 45. If it doesn't engage then try some more taps on the brake. Not the best system which is why they added a switch in 2015 model.
Maybe Nissan has implemented a similar system in the Titan XD.
 

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About the Exhaust Brake, or lack thereof.

Apparently the big Ford diesels didn't have an on/off switch until 2015. Here's a description of how it used to work from another forum:


Maybe Nissan has implemented a similar system in the Titan XD.
I posted a thread about this, a Canadian publication eluded to a downhill speed control as part of the tow/haul system.

It is possible that a switch was not included because an exhaust brake with good holdback can cause traction issues in certain conditions.
 
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