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Discussion Starter · #1 ·
I have a 22 fwd version so turbo 3 cylinder and has eco/std/sport for the modes.

Today I drove home from work now back to work with the boost gauge screen displayed. I took the freeway home traveling 80 and the surface streets to work just now traveling up to 55.

What I observed on the gauge I found interesting and thought I would share. I must admit that I did not pay all that much attention to the compression side of the screen and will need to do this again while noting the compression ratio vs the boost.

All of this was while in active cruise control. In standard mode the boost was staying real close to 0. Only dipping slightly below and going slightly above depending on flat or tiny up hill/ down hill. When in sport mode the rpms kicked up and it never went into boost. In eco mode it kept similar rpms as the std mode BUT was always in boost. It looked to be around 5 to 8 psi most of the time.

On the surface street I was also using cruise but encounterd some slow down speed up times do to more cars around me and stop lights. I did not pay as much attention this drive since I needed to pay more attention to the road and fellow cars. It pretty much mimicked the freeway but at lesser levels of boost and rpm.

In the morning I hope to repeat this and see the compression ratio changes that go with these same situations. There will be more cars on the freeway though so I may not be able to look long enough to really take good notes.
 

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Discussion Starter · #2 · (Edited)
Yesterday I finally started a mpg comparison in relation to the speed and modes mentioned in the previous post. I still need to test sport mode and that should happen tomorrow.

Same rules apply from above. Cruise control set to 80 on the same stretch of freeway but this time resetting the mph avg right when I get up to speed. The final avg is after a roughly 8 mile stretch of freeway when changing to the next freeway. I get off the first exit of that second freeway and the speed has to change for the exchange ramp and off ramp and of course the surface streets. Thus, I noted the mpg at the entrance to the exchange ramp.

Yesterday was Standard mode. I ended up at 33.8. Today was ECO mode. Final was 32.7. I never had to deviate from my speed for either run. Yesterday I had a couple times where a slower car moved in front of me but before the adaptive cruise could adapt I moved over to an empty lane. Today that did not happen. The changing lanes never made me change speeds so it should be apples to apples still.

The 1 mpg less in ECO mode makes me wonder what will Sport mode end up at. Remember what I noted above about the boost vs compression ratio vs rpms. It seems like all that boost in ECO mode slurped a little more gas than the nearly zero boost of standard mode did at 80mph. Slower speeds might show a reversal of these numbers. Heck Sport mode may throw a wrench in this even at 80. I shall see 23 hours from now.

For the slower speeds I will need to find a long road with no traffic lights. The amount of time sitting at a light is too variable to do this kind of comparison imo. Especially with 19 lights in 8 miles. I have never had a day where I did not sit at several lights but I have had days where I hit just about every one of them. Like I said, too big of a variable.
 

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I'd be interested to see the same test on a route demanding lots of on-off pedal at lower speeds, like flooring it between stop signs on a residential street with one at every corner. I suspect that's where eco will give the best results, but if it's a timed run I also suspect slower times.
 

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I’m perplexed at the application of boost? Seems to be counter intuitive, coming on in eco mode, and not as revs rise?

is the variable compression at work, or something else?
 

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is the variable compression at work, or something else?
That's the big mystery with these things, figuring out exactly how the turbo and VC interact. Nobody has. That's the reason there are still no tunes for the KR20 Altima turbos even though they've been out for 3 years. I could see Eco mode going to a very low compression but ramping the boost up slightly to not waste energy spinning it up, that might pay depending on the intake and exhaust architecture. But I'm sure some guy in the basement at Nissan Engineering is the only person on earth who knows the answer, and he doesn't seem to want to talk.
 

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Discussion Starter · #6 · (Edited)
Some may already know this but for those that do not...the only numbers showing on the boost gauge are -15/0/15/30 so what I am about to say is all based on estimating the boost based on where the needle is at a given time. It shows as a circle which allows it to be looked at like a clock. Every minute on the clock is the same as one PSI of boost on this gauge. The VC is shown as a slide rule in the vertical plane with no numbers at all. It shows Power on top and ECO at the bottom. In Power mode the VC will be on the low side to allow for high boost levels while the ECO side is the High Compression side that is used with low to no boost. The higher VC is best for gas milage. I read up on this feature and found it stated to range between 8.x:1 to 14.x:1.

At idle the VC sits slightly above the middle marker putting it slightly on the low CR side of things. When the boost is below what looks to be around 4-5 PSI the VC will stay in ECO VC, aka high compression ratio. At 1-2 PSI it will max it out at the 14:1ish area. From 3-5 the VC is still in the ECO side but is heading towards center. Above 5 psi the VC moves to the center and up to Power VC mode as the boost increases.

This relationship between boost and VC is what I would expect and does not seem to be a mystery. At least not to me. This being because it is well known that the lower the compression ratio the more boost you can safely run. Boost and high compression do not play well together. So yeah this relationship is as expected. The unexpected thing for me is the vehicle modes vs using boost or RPM to generate the same amount of propulsion energy to maintain the same speed. I did not expect ECO mode to ALWAYS be in boost. But it does somewhat make sense from a power to weight ratio standpoint.

My last vehicle was a Silverado Trail Boss with the 5.3l v8. They also come with a 6.2l v8 if optioned. The 6.2l is EPA rated to average 1-2 mpg lower than the 5.3l and makes 65hp and 80tq more than the 5.3l. But real world driving proves that with normal driving habits the 6.2l actually will average 1-2mpg MORE than the 5.3l. This, I believe, is due to the higher power to weight ratio of the 6.2l allowing it to not work as hard to provide the same amount of propulsion energy. Basically the lower power engine needs to work harder to move the same amount of weight. Applying this thought process to the testing of the modes on the Rogue, I would expect the higher rpms make more power but then again, so does more boost. Since my testing on the freeway was at cruise each mode needed to make the same amount of energy to keep the car at the same speed. Each mode had to use something different to make the same power level due to the rest of the tune for that particular mode.

To understand the RPM vs boost for the modes we need to consider other parameters for the engine and trans. The main thing here is the tuning for each mode. Sport mode tune is more aggressive, performance/power wise, than standard and ECO is tuned for the least performance/power. One of the ways this is done is via ignition timing where they advance timing to achieve more power and retard the timing to reduce power. This is similar to boost in how it helps keep an engine safe at higher power levels. Another item is the variable cams which also work to increase power or maximize fuel economy. There are a multitude of things they can tune/adjust to achieve more power vs more mpg. A primary part of their tuning is always to keep the engine safe while providing the desired results of either power or mpg.

With this in mind, I would expect that in Sport mode they have advanced the timing and the intake cam to achieve the most power with AND without boost. Of course when boost levels increase the timing will be retarded. But probably still less so than when in ECO mode. As RPMs increase, propulsion energy also increases for a given tune. This is likely why they do not need boost to maintain the same propulsion energy level to maintain the same speed.

At lower speeds and on off throttle, I too, expect the ECO to EEK out the most MPG. But heck yeah it will take more time. I wonder if the lack of aftermarket tunes for the 4cyl VC engine is due to tuners not knowing how to safely work with the VC itself? The tuners know timing and compression relationship to boost but a varying compression ratio is a much lesser known item in tuning.
 

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I wonder if the lack of aftermarket tunes for the 4cyl VC engine is due to tuners not knowing how to safely work with the VC itself? The tuners know timing and compression relationship to boost but a varying compression ratio is a much lesser known item in tuning.
Personally I think it's more a case of multiple controllers being involved and the electric IVT having its own controller. I agree it's easy enough to plot compression vs boost, but as you mentioned rightly, those aren't the only factors. Add to that needing to tune a whole second brain (three if you include the TCM, and if you watch it climb hills with the cruise on, you'll understand why that probably must be included), and you have what Newton called a "3 body problem". Break out your supercomputer. ;)
 

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Discussion Starter · #8 ·
I did the Sport mode today. Before I state the results, I need to mention that I encountered a variable that is out of my control on this drive cycle. That variable was Mother Nature. She decided to blow in some rain clouds and while it did not rain, they trapped in some heat and added some humidity. Temps were 79 and 80 on the first two days and 85 today. Humidity was 16%, 12% and then today was 33%. This may not make any difference at cruise but thought I would mention it.

....and the magic number was...33.2.
 

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Say, my 2022 Rogue with the 3 Cylinder turbo just started making a strange whirring noise coming from the engine, start to hear it around 35 mph. It changes its pitch/cadence during acceleration vs deceleration. I turn the HVAC completely off while hearing it, nothing changes, so I don't think it has anything to do with the AC compressor. Any ideas on what I'm hearing?
 

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Say, my 2022 Rogue with the 3 Cylinder turbo just started making a strange whirring noise coming from the engine, start to hear it around 35 mph. It changes its pitch/cadence during acceleration vs deceleration. I turn the HVAC completely off while hearing it, nothing changes, so I don't think it has anything to do with the AC compressor. Any ideas on what I'm hearing?
Get a video clip and post the URL here on the forum for us to listen to it.
 

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Get a video clip and post the URL here on the forum for us to listen to it.
Doubt you could hear it on a vid clip...I'm leaning towards it having to do with the turbo, because after 3 months of not hearing it, it started after the very first time I had to really kick in the turbo to get around some traffic. I'll monitor it for a bit longer and take it into the dealership to have them assess what it could be.
 

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Alternator clutch? Wow. So many things to learn about this platform and nowhere to read about it
Yah, just about everything Nissan has an overrunning clutch built into the alternator pulley. Some of them can be whiny enough to be noticeable. That doesn't necessarily mean it's failing, most of the time it's simply a clutch that's a bit noisier than typical.
 

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They're part of the alternator assembly as far as Nissan is concerned and the info in the FSM's is pretty sketchy. Aside from noise (and a failing one can make very rude noises), symptoms of a bad one are undercharging (if it's slipping) or intermittent belt squealing (if it's locking up).
 

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VStar, was this response above (alternator clutch) ref my "whirring" noise heard on my rather brand new 22 Rogue?...or were you commenting on another's post?
Yep, that was about your noise. It's an overrunning clutch, and I think I've heard them make dang near every sort of noise a rotating mechanism can make. Whining, buzzing, burping, squealing, scratching, and lots of etceteras.
 

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I was referring to information sources about the 2022 rogue in general for DIY situations and general knowledge beyond changing the oil, etc.
Nissan isn't doing PDF manuals anymore, everything north of '16 is HTML and online only. You can get prepaid access to the FSM's and WD's, but it's like $18 for a day and big numbers for a month or a year.
 
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