Cummins 5.0L Turbo Diesel Potential - Nissan Titan XD Forum
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post #1 of 56 Old 01-12-2016, 12:19 PM Thread Starter
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Cummins 5.0L Turbo Diesel Potential

So I've been reviewing the ISV 5.0 and wondering how much headroom they have built into this motor.

After a bit of research, I'm guessing not much. While I'm no mechanical engineer or diesel expert, I've been looking at all the info flowing around on the ISV.

You'll find quite a bit of the thought behind the M2("M Squared") Turbocharger here:
http://www.cumminsturbotechnologies....at_Dresden.pdf

As a reference this is how the M2 is laid out:



For Source, see Note 1
Light Green=Rotatory Turbine Control Housing and Low Pressure Turbine, Exhaust Side
Blue=High Pressure Turbine, Compressor Side
Yellow=Low Pressure Turbine, Compressor Side
Dark Green=Rotatory Turbine Control Valve Controller and Valve
Brown=High Pressure Compressor Bypass
Grey=High Pressure Turbine, Exhaust side, Outlet Piping


Firstly, I do believe they have done a very good job optimizing this engine.

The real challenge is meeting stringent emissions requirements while meeting goals for durability, power delivery, packaging and fuel economy.

If you have looked at the M2 ("M Squared") compound turbocharger, you will find quite an innovative bit of engineering. It's not a twin turbo, but two turbos in one assembly, working at times independently and in concert to produce boost, reduce lag, facilitate EGR functionality, DEF regeneration and perform waste gate functions. They are basically doing with two turbos what a single variable geometry turbo can do. They claim packaging and efficiency advantages. The interesting part is the rotary turbine control valve. It is essentially a diverter valve that controls where the exhaust stream goes. It's able to split the flow between the high pressure (smaller) and low pressure (larger) turbos. Additionally, it can restrict exhaust to facilitate warm-up, EGR and regen functions and it can act as a waste gate. I also believe it could be programmed to act as an exhaust brake, but for some reason, Nissan and Cummins chose not to do so.

So looking at what is available, I have done my best to recreate the HP and Torque curves, just to see what is really going on here. Cummins gave us a look at the torque delivery several months ago. From that we can extract HP.



While not exact, it's quite close. What is shows is a very flat torque curve across a broad range staying in the 550lbft range from 1600 to 2800 RPMs. Peak HP is at 3200 RPMs but is above 290hp from 2800 to around 3500 RPM.

So while diesel folks make a big deal about torque, the ability of the engine to actually do work is measured in HP. What makes a diesel so special is its ability to make lots of torque quickly, thus producing meaningful hp before it hits peak hp.

In this engine, what is remarkable is the range across which it maintains torque, equating to steadily rising hp from peak torque to peak HP.

So why is that interesting? For towing, it means the engine remains capable of delivering near peak power early and across a broad band. This reduces shifting and allows for a more relaxing experience at peak power levels. In fact, the trend is towards larger number of gears, to keep power delivery consistent and flat, eliminating lagging and peak areas of power delivery for a given engine. Thatís why you generally see the HD diesel pickups lagging in gear count over gasoline engines. Today's light duty diesels just donít see as much benefit for the additional ratios as gasoline engines do. Even Ford EcoBoost engines, which are a model of gasoline power delivery, are getting more ratios. Again, this is about deeper overdrives for unloaded cruising, while allowing the engine to remain in an optimized power band during high load situations. GM's 6.2 saw significant improvements in loaded performance from the addition of an 8 speed. But there is a cost, and that is in the transmission's propensity to hunt gears as loads change. With great transmission tuning, it can work, but if things are less than optimal, there can definitely be a franticness to the transmission's performance.

That said, having seen the videos of the XD at highway speed, I'm a bit surprised that there isn't a higher overdrive or lower rear axle ratio available. Obviously Nissan is trying to allow the XD to tow in top gear. They could add a 7th gear and probably drop RPMs at 70 from nearly 2000 to around 1600 and still produce adequate power (about 160hp) for light load driving. There would be a jump in economy, but it would be at the cost of either gear hunting, or locking out the final OD when towing. My guess is that we will eventually see seven speeds in the diesel XD when Nissan finds the right transmission.

Now back to power. How much is left is the ISV? My guess is that Nissan and Cummins left some headroom. If you look at the M2 modes of operation, you'll see that they start modulating the waste gate at high engine speed and high torque operation. This suggests they are dumping exhaust to either limit peak boost or LP turbine rpm. Either way there appears to be some more boost to be had at higher RPMs (Green area of the graphic below). It could be at the cost of durability, or Nissan/Cummins could have chosen to keep some boost in reserve for high altitude operation. If that can be tapped, you could potentially see a bit more torque and power from 3000 to 3400 rpm.


For Source, see Note 1

And here's how the modes work:


For Source, see Note 1

But if you are thinking that there will be a 400hp version or even a 400hp tune, I think you are wrong.

Overfueling this engine will not be an option due to the emission controls. So fueling and boost will have to go hand in hand. The only real benefits will be had at or near peak HP or around 3200rpm. I donít think that they will try to extract more rpms from this engine given its lofty 4000 rpm redline. As is, torque drops off dramatically after 3600 rpm and the extra revs donít accomplish anything as output above 3800 rpm drops below 290hp as is.

If they can extract 10% more torque from the engine at 3200 rpm, by reducing and delaying wastgate operation, then you would see peak torque move up in the powerband, and HP increase. But I donít know if the engine or other components would be up to the additional boost or if the LP turbo is capable of it. If this is possible, I can't see hp rising much above 340hp or so at 3200 rpm.

The point is that increasing torque significantly is not really going to be possible, particularly in the lower power band as the HP turbine is doing all it can. You may be able to get more out of the LP turbine which would significantly increase torque in the peak HP range, but peak torque would only increase modestly.






To get larger gains, you would have to start modifying the M2 turbo. The real issue is the LP turbo packaging. It's not easily replaceable as some of the larger diesel turbos are. Maybe modifications in materials and impeller design can yield some additional performance, but more boost will require larger turbines, which will require a new and unique housing. I don't see the aftermarket clamoring to do that given the limited production. Maybe Cummins will tweak the design down the road.

So for tuning, there may be some wiggle room in delaying waste gate operation and adding fuel with the additional boost, the gains won't be as dramatic as diesel tuners usually claim. And given the delicate balance of turbo, rotary turbine valve and emissions operations, there may not be anyone lining up to try it.

The only aftermarket engine part so far is the Banks intake. I can't see that really doing much for power as the intake is not restrictive to begin with. The more critical airflow areas are contained in the mess of tubes that is the M2 turbo.

What I'm really hoping for is the addition of the exhaust brake programming, continued refinement of the M2 turbo and, potentially down the road a 5.5 to 6 liter variant of this engine. NV2500 anyone?

Note 1: Source: "Development of Cummins Turbo Technologies Integrated M2 Two-Stage Architecture using Rotary Turbine Control (Holset RTC) Technology for the Cummins 5.0L V8 Turbo-Diesel Engine"
D. Brookshirea, N. Manoharana, J. Lovea, N. Khannaa,
and Cummins Turbo Technologies
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post #2 of 56 Old 01-12-2016, 01:12 PM
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Interesting write up, though you're glossing over the advantages of compound turbos and erroneously comparing them to VGT/VNT turbos.

You also didn't cover head design, valvetrain arrangement or bore and stroke.

Nice work finding that material too!

I don't agree with your assessment. In my opinion the ISV with the m2 arrangement could run as high as 400hp before needing supporting modifications. Due to the M2 system and what appears to be tuned intake.
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post #3 of 56 Old 01-12-2016, 01:50 PM
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I'll guarantee 400hp from it, stock injectors and turbos. I don't know what the primary (low pressure) or secondary measure out at, so hard to say what it's ultimately capable of.

400hp from the engine alone will be a cake walk. However, you DID hit on one thing: emissions. Emissions-present tuning is the wave of the future, however it seems thus far it's not what folks are doing. Deleted, this thing cranks 400+, maybe even 400+ at the wheels. All dependent on tuning options.

And that Aisin is going to hate life....
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post #4 of 56 Old 01-12-2016, 02:27 PM
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I think that's why they put the big aisan behind the ISV, so when it gets turned up to 400hp the transmission doesn't give up. A truck that lasts with modest tuning will build a good reputation for Nissan.
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Originally Posted by NavyCuda View Post
Interesting write up, though you're glossing over the advantages of compound turbos and erroneously comparing them to VGT/VNT turbos.
The comparison with a variable geometry turbo is valid. While each has advantages and disadvantages, they both serve the same purpose, that is to provide the levels of boost needed for the high specific outputs of today's diesels while minimizing lag and surge. As an added bonus they assist in emissions control and warm-up etc. They go about it in different ways. Cummins says this much as well, although they state that the main advantage of the compound turbo is higher boost across the entire powerband, which seems evident. But you can plug in a VGT turbo in the place of the M2 as Cummins does in their non-Nissan ISV.


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Originally Posted by NavyCuda View Post
You also didn't cover head design, valvetrain arrangement or bore and stroke.
Yes. I did skip that. This isn't intended to be a dissertation on the entire engine, just the bits that can be tweaked through tuning to provide more power. My assumption is that, with the possible exception of the 4 bolts per cylinder design of the head, the block and heads have a lot of untapped potential. The over-square bore is particularly interesting to me, but thats another thread.

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Originally Posted by NavyCuda View Post
I don't agree with your assessment. In my opinion the ISV with the m2 arrangement could run as high as 400hp before needing supporting modifications. Due to the M2 system and what appears to be tuned intake.
I hope to be proven wrong here as I would love to see either Cummins or the aftermarket make magic with just tuning, but to get to 400hp is a huge step. There would have to be some serious boost left as getting to 400hp would mean torque of 660lbft at 3200rpm (right now to make 310hp at 3200rpm they are producing 510lbft). At that RPM, its all on the LP compressor and the HP compressor would be well beyond its limits. And that is the secret to this engine, maintaining torque at higher RPMs is where the peak hp comes from. So to get 400hp at 3200rpm requires a 30% increase in torque over stock at that speed. Maybe you could do that by overfueling, but the emissions system wouldn't last very long and EGTs would be an issue. I haven't seen the boost figures for this engine, so maybe that LP turbo has some capacity left but I can't image they can find that much additional boost in the LP single stage mode. I suppose it all depends on if and how much they are waste-gating at peak hp.

At any rate, if they did manage to pull that off, assuming no changes to the high pressure turbo side of things, the torque and HP would look something like this:



The transition from HP to LP is now quite apparent.

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post #6 of 56 Old 01-12-2016, 03:21 PM
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In regards to VNT/VGT verses compound/series is that compound turbos always have better density ratios. If the LP and HP turbos are sized correctly, there will be plenty of headroom without getting too far outside the efficiency island.
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Originally Posted by NavyCuda View Post
I think that's why they put the big aisan behind the ISV, so when it gets turned up to 400hp the transmission doesn't give up. A truck that lasts with modest tuning will build a good reputation for Nissan.
Physically, it appears the Aisin can take it and much more.

Problem is there isn't any tuning available for the Aisin to full reap the benefits. Last I checked, they are pulling fuel on shifts in the 6.7 trucks to keep the Aisin happy. Admittedly that's been a number of months.

And of course, 400hp crank and 400hp wheel are very different; we typically refer to wheel most of the time in aftermarket tuning.

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If 400whp isn't attainable with this motor with just tuning (& delete if need be) this truck will be a huge flop IMO since the payload/ towing numbers are not that impressive (even compared to current 1/2 tons) it would still appeal to a large group if you could get lots of reliable power for not much $ in the aftermarket. As far as emissions equipment goes the only word that comes to mind is DELETE!..
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post #9 of 56 Old 01-12-2016, 11:50 PM
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Banks, bullydog and other will have tunes for this motor. Also the tunes chang the parameters of the ecu meaning over fueling is not detrimental to the motor. Also you can regen when u want. A Def delete would-be to most optimal for this truck. All the new trucks would benefit from delete packages. Yeah rolling Coal is cool but modest smoke keeps the motor within speck. To much fuel does not burn witch keeps it cooler then running lean. You will never seize a motor over fueling it. There will be a stock, 40hp, 90hp and more runes for this. Look at a duramax lly they have a 120hp and 200tq tune. It's been there for ever. It's just when you get to thar stage you need to update students bolts, injectors, fuel pumps, rails, exct. Also I that rune hp and tq is at the wheels. So a 80hp 100 tq is like a 430hp 700 tq on motor
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post #10 of 56 Old 01-19-2016, 01:50 AM
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After driving this truck home tonight and on the test drives there is definatly potential in this 5.0 making power. A simple " emission" tune will give it a nice boost but.... put in a delete kit and a nice smarty or efi live tune and this will go like a raped ape, very easy to get that 400+ rwhp if you have your boost and fuel dialed in... Only thing that will hold it back is the aluminum heads but thats what studs are for.
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