edporsche

I'm sure most of you have seen this already, but I just saw it tonight. It shoes how the COD works in great detail. It's more robust than I originally thought. It also changes cylinders when going from 8 to 4. I had assumed it would always pick the same 4 to shut down, but nope. Also, the roller cams looks really cool. It's a stunning engine by any measure.

DeerHunter

Interesting video - thanks edporsche. I don't see anything there that shows randomization of the deactived cylinders. In fact, the technical write-up I have in my hand states:
Still, it's a pretty cool piece of tech.

edporsche

I was using the colors of the cylinders during the sequence. It appeared that the colors changed from cylinder to cylinder. I also thought that all 4 cam shafts appeared to have the same sleeve for all cylinders. I don't have any real data. I gleaned it from the video. Where did you get your information?

After carefully reviewing the video again, I can clearly see that some cylinders do not have the sleeve which decouples the intake valves. Thanks for clearing it up.

DeerHunter

Here you go - see page 4 for an illustration and description.

HyperS4

So here are my questions based on this technical feature:

1) I am stuck in traffic most of the time on my commute to and from work and I can see that 80% of the time Im in 4-cyl mode. My concern is that I am wearing those "active" 4 cylinders 80% more than the deactivated cylindars. If after a year of driving this way, will those 4 activated cylindars be more worn out with gunk and muck and put strain on the deactivated cylinders when I actually do spirited driving?

2) Is the hesitation I feel while in gear at slow speeds the effect of the car trying to figure out if it should stay in 4cyl mode or transform into the 8cyl mode? Sometimes I get jerkiness while still in gear without any gear change and I feel this has to do with the cylinder deactivation(or reverse).

I wish there was a way to keep it in 8cyl mode all the time just to see if there really is a tradeoff for mpg. I wonder if this can be vag'd.

DeerHunter

Cylinder on Demand depends upon the following parameters:

• Low to mid-range engine loads (118 to 184 lb-ft of torque)
• Engine between 960 and 3,500 rpm
• Coolant above 86F (30C)
• Third gear or higher
• No major steering or throttle inputs

Based on your description, it doesn't sound like cylinder deactivation is the cause of your symptoms.

As for the wear issue, I wouldn't worry about it. The pistons are still moving up and down in all cylinders and wear will be approximately equal.

HyperS4

Actually, based on my driving, and those parameters listed above, I am definitely in the deactivation mode 80% of the time. The car gets into 3rd gear by 15mph and my avg speed on my commute is 35-40mph typically in 6th or 7th gear depending on the uphill gradiant. This would definitely put the rpm around 1200-1500 also.

However, even though the pistons are still moving up and down, theres no gas being fired. Therefore theres nothing being burned to expel any residual crap that would attach to the pistons/cylindar walls. So the they actually do stay cleaner in the long run than the ones that are constantly running regardless of 4 or 8cyl mode.

DeerHunter

It's possible that they'll stay cleaner but, given the low-load conditions, I doubt it'll be anything significant. Moreover, even if the other four cylinders became more gunked up, they won't be more strained since they will receive the same amount of air and fuel as they would on a brand-new motor.

Regardless, keeping half your cylinders comparatively clean would be a good thing. Think about the extreme case of burnt valves. Would it be better to only have four burnt valves (one per cylinder) or eight? The latter might represent equal wear-and-tear, but the engine will run the worse for it.

HyperS4

I am revisiting this thread because I did some actual watching of my dash to see how often I get into 4cyl mode. It seems not often...

The biggest factor for me is that my engine temp doesnt warm up practically until Im a couple miles from work(10 mile commute). So Im in 8cyl mode the whole time while stuck in traffic.

I cannot complain anymore for having an average of 17mpg since picking up the car then.

mwar99

You need a longer commute

I am averaging probably around 23 mpg on my way into work and about 19 mpg on the way home. Difference - down hill to work and up hill home for about 22 miles each way. After the snow last week when people were driving slower I actually averaged 26 mpg on the way into work.