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Discussion Starter · #1 ·
The MO is a great car and my parents recently bought one and love it. They have been averaging about mid 20s fuel economy with even 27mpg on the highway! I think this is really incredible for a 4000lbs vehicle. I think the CVT plays a big role and puts the MO beyond other SUVs in fuel economy.

Other manufacturers are also doing things to improve economy. The new Odyssey mini-van achieves 21/28 mpg fuel economy! This is because they have a system that shuts of 3 of the 6 cylinders when the engine is cruising down the highway or any relatively low stress situation. Apparently the other cylinders fire up instantly when needed and the driver doesn't even notice any difference between this and a standard engine.

What if Nissan added this technology to the MO. Imagine, I bet the fuel economy would be even higher than the odyssey...maybe like 22/31 or something. Imagine that! It would really be cutting into the hybrid SUV type fuel economy. I wonder how one can recommend ideas or suggestions to Nissan.....
 

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Dodge is doing the same thing (cutting out half the cylinders) on their HEMI for certain vehicles like the Magnum, which brings it down to just being a gas guzzler rather than a frickin' black hole! :D
 

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Corin said:
Dodge is doing the same thing (cutting out half the cylinders) on their HEMI for certain vehicles like the Magnum, which brings it down to just being a gas guzzler rather than a frickin' black hole! :D
The 5.7 litre V8 Hemi on the Magnum R/T, 300C and Charger R/T do that... I've looked at a Magnum as an alternate to the Murano. If you're into V8's, it's an interesting option. I did test drive one, and I have to admit, the quiet V8 burble I heard while it was idling took me back to older days and sent a chill down my spine.

Have your cake and eat it too. You can't tell when the MDS is in action, it's totally transparent.

That would be a great feature on the Murano. (Along with the V8 and 100 more HP!)
 

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Caddy's did that way back.
It wasn't so nice for their engines.
I guess they have figured out to keep the block from twisting being that is goes from being heated evenly to unevenly. The poor spark plugs must get awful filthy too. There are a lot of things to worry about when engineers make engines drop cylinders....do they open the valves so there isn't any compression dragging the remaining cylinders?
Things that make you go hmmmm...
 

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mgthe3 said:
Caddy's did that way back.
It wasn't so nice for their engines.
I guess they have figured out to keep the block from twisting being that is goes from being heated evenly to unevenly. The poor spark plugs must get awful filthy too. There are a lot of things to worry about when engineers make engines drop cylinders....do they open the valves so there isn't any compression dragging the remaining cylinders?
Things that make you go hmmmm...
Mgthe, I agree!
I am afraid that someday, one or two of the cylinder(s) got deactivated and will never turn back up. :2:
 

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Early incarnations of shutting off cylinders just disabled the same cylinders every time. With coil on plug technology and the computer coordinating controlling the ignition system, the disabled cylinders are cycled through the entire engine, keeping the block temperature consistent and cooler, which in the event of coolant loss or extreme temperatures will help save your engine.
 

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In the end, you can get good fuel economy if you really change your driving style to be super conservative. That means accelerating at the same rate as other cars, coasting a lot when coming to a stop sign or red light, and never going faster than 65 on the highway.

I think cylinder deactivation technology is great, but I'm not sure how the CVT will handle it. Remember its a push belt system and it experiences more load at lower revs (where it is operating at a higher ratio and there is less torque from the engine - think about a manual transmission and trying to accelerate from 5th gear instead of 3rd). I can imagine cutting half the cylinders out would really push the CVT even more under conditions where cylinder deactivation would prove beneficial (i.e. steady speed cruising).
 

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GM has finally gotten into the act. The new Impala SS has 305 HP but gets 28MPG because of Displacement on Demand. The same technology is going into the new Tahoe/Yukon. The 5.3 liter V8 with DoD and a new 6 speed transmission reportedly averages 21MPG for the RWD version..

21 MPG is outstanding in a vehicle that large. I hope those numbers hold up in real life because a large SUV with that kind of fuel economy will probably sell well for GM. (GM didn't say whether those are real world numbers or EPA numbers) GM is also planning to add a diesel V6 to the Tahoe lineup in the 2007 MY.
 

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Discussion Starter · #10 ·
I think cylinder deactivation technology is great, but I'm not sure how the CVT will handle it. Remember its a push belt system and it experiences more load at lower revs (where it is operating at a higher ratio and there is less torque from the engine - think about a manual transmission and trying to accelerate from 5th gear instead of 3rd). I can imagine cutting half the cylinders out would really push the CVT even more under conditions where cylinder deactivation would prove beneficial (i.e. steady speed cruising).

I think a CVT can be compared to a multi-speed bicycle. I think current bikes have about 24-27 speeds. Now imagine pedaling at the same rate and keep shifting gears such that the pedal rpms don't change much but you start going faster. CVT is just like a bicycle with a million speeds. The chain is analogous to the CVT belt. The gears in the front and rear of the bicycle are analogous to the CVT pulleys.

Using this analogy, I don't understand how it's like a car trying to accelerate in 5th gear V. 3rd gear?

I also don't understand how there is more load during start situations. Sure acceleration causes load on the CVT versus just cruising at a constant speed. What does low speed have anything to do with it? Accelerating from 40-60 will cause more load than accelerating from 0-40 even with the same amount of throttle applied.

Finally, how does cutting off half the cylinders have anything to do with more stress on the CVT? Cutting half the cylinders is like have a 3 cylinder engine which is weaker...this will actually cause less stress on the CVT, not more.
 

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Kan-O-Z said:



I think a CVT can be compared to a multi-speed bicycle. I think current bikes have about 24-27 speeds. Now imagine pedaling at the same rate and keep shifting gears such that the pedal rpms don't change much but you start going faster. CVT is just like a bicycle with a million speeds. The chain is analogous to the CVT belt. The gears in the front and rear of the bicycle are analogous to the CVT pulleys.

Using this analogy, I don't understand how it's like a car trying to accelerate in 5th gear V. 3rd gear?

I also don't understand how there is more load during start situations. Sure acceleration causes load on the CVT versus just cruising at a constant speed. What does low speed have anything to do with it? Accelerating from 40-60 will cause more load than accelerating from 0-40 even with the same amount of throttle applied.

Finally, how does cutting off half the cylinders have anything to do with more stress on the CVT? Cutting half the cylinders is like have a 3 cylinder engine which is weaker...this will actually cause less stress on the CVT, not more.
When I first heard of this idea, I didn't understand it either, but there was a thread where it was clearly explained, that higher revs = less strain on CVT. It was a thread I think that threw a wild idea around that we should all drive around in Ds all the time. I'll try to find it, but meanwhile you can do a search.
 

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Eric L. said:


When I first heard of this idea, I didn't understand it either, but there was a thread where it was clearly explained, that higher revs = less strain on CVT. It was a thread I think that threw a wild idea around that we should all drive around in Ds all the time. I'll try to find it, but meanwhile you can do a search.
For a given speed, higher rpms means the transmission is in a lower gear which puts less stress on the CVT. It is like pedalling a bike up a
hill in a high gear instead of a lower gear. You pedal slower in the higher gear, but the stress in the chain and your legs is greater.
 

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Discussion Starter · #14 ·
Ok I understand what you are saying. It's like pedaling a bike going 5 mph in first gear versus pedaling a bike going 5 mph in 27th gear. Yes I can see the chain has more stress on it on the higher gear but you pedal much slower. Here are my comments:

-This idea is true for any transmission. A lower gear will produce less stress on a CVT or conventional gears or a chain. This is only assuming you are going constant speed and not accelerating. Most transmissions are in a low gear to accelerate so this argument is moot unless you manually override like in Ds/Dl and just cruise at high rpms.
-In most CVT cars, you cant really be in a 'lower' range unless you have some sort of sport mode that even the SE model doesn't have.
-I believe the CVT shifts from the stress on it...for instance, you are in a high gear and press the throttle to pass...the stress becomes greater so the CVT automatically shifts to a lower range. I guess what I am saying is that the way the computers shift the CVT, the stress level on the CVT is probably almost the same:
1. Accelerating from start. CVT is in low gear so transmission is in a low stress mode but acceleration and torque from the engine puts more stress on the CVT
2. Crusing at a constant speed in high gear will produce more stress on tranmission but the engine will apply less stress than accelerating.

In normal conditions, stress on the CVT comes from the engine. The engine at higher RPMs means that more throttle is being applied and hence the engine is generating more torque and hp thus putting more stress on the CVT. The CVT will downshift relieving some of that stress.

So I don't really think that the higher gear/more CVT stress is an issue. Also remember at lower gearing/higher rpms, the engine and CVT are both under stress whereas at higher gearing/lower rpm...perhaps only the CVT is under stress and engine is not.


Finally, I dont think the 3 cylinder technology would affect the CVT in any way. It would work perfect IMO.
 

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Kan-O-Z said:
-In most CVT cars, you cant really be in a 'lower' range unless you have some sort of sport mode that even the SE model doesn't have.

So I don't really think that the higher gear/more CVT stress is an issue. Also remember at lower gearing/higher rpms, the engine and CVT are both under stress whereas at higher gearing/lower rpm...perhaps only the CVT is under stress and engine is not.



The SE has six fixed ratios so you can be in a lower range if you desire.

The engine is under more stress under high loads which is when you have a gear ratio higher than optimum. For example, a car going up a hill in high gear can lug the engine causing pinging and overheating.
 

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Kan-O-Z said:
The engine at higher RPMs means that more throttle is being applied and hence the engine is generating more torque and hp thus putting more stress on the CVT. The CVT will downshift relieving some of that stress.

The idea from the other thread was that the opposite is true. Higher RPMs = less stress on the CVT belt for a given speed.
 
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