New Honda Pilot VCM engine

[Schmoe]

Was waiting for my 02 Accord to have some warranty work done and sure enough, a salesman got ahold of me. Let him talk his talk but got a free test drive on a Pilot out of the deal. This has the new VCM 3.5l engine that effectively cuts off one bank, not alternative, cylinders. This is a V6. That thing kicked on a lot while driving. You could feel it. It was akin to downshifting. One question that I have after reading the literature, they state that when the VCM is activited, the pistons keep moving, but the exhaust and intake valves remain closed. How does that work exactly? Wouldn't having the valves closed make the engine work harder...i.e. as in compression breaking?
Liked the Pilot and think Honda knows their stuff, but I have memories of the old 4-6-8 GM engine in the 70's that absolutely $ucked.

 

[Dad2leia]

Schmoe, what exactly did that feel like while you were driving it? My wife and I were considering a Pilot as our next vehicle, but that is a couple of years down the road, so maybe this system wouldn't be a factor, but am curious anyway.

 

[javacontour]

Schmoe,

I googled this and basically the cam follower still follows the cam but doesn't act on the valves when the solenoid kicks in for the VCM function.

T

 

[T-Keith]

Similar to other systems like GMs or Chryslers it closes the valves and allows the trapped air, to act as a spring. The V8-6-4 was very similar, but primitive computer systems of the day were inadequate and the gain was not good enough to justify the roughness.

From what I've heard most of the new systems are transparent, but I haven't driven one.

-T

 

[PandaBear]

I have heard that Accord Hybrid uses active acoustic noise cancellation and active hydraulic engine mount to make the car quieter and vibrate less with VCM on.

Sounds like the technology is not yet mature but usable. I would rather get a 4 bangers instead. 1 Cyl of difference is not worth the fuel saving, vibration, noise, higher initial cost, and more parts to fail down the road.

 

[javacontour]

I wonder if they can time when the valves close and then use say a partial charge of air in the cylinder to act as a damper to smooth out the engine when it goes from 6 cylinders to three.

I doubt this works on each cylinder individually, so perhaps they just pick a place in the cycle where the volume of "air" in the deactivated cylinders balances out. As pressure rises in one or more cylinders, it is falling by a similar amount in the others. I don't know if you can make this totally even out for an odd number of cylinders or not, and I don't have the time to look at it right now. Perhaps someone already knows.

I can see closing the intake valves so the air metering is correct.

However, why not leave the exhaust valves open so you don't have the compression braking effect?

Just thinking out loud, I really don't have any solid answers.

T

 

[Schmoe]

It felt like there was a .5 sec hesitation. I mean, you could feel it. Then if you pressed on the pedal hard enough, you'd have the slight hesitation and then the downshift. It was noticable. I was rather surprized. What I wonder about is, exactly how this works. There has to be some sort of mechanical link that either disengages the camshaft or valves. Then, they stay in the full up position. Like I said, I think Honda engineers are a class act, but this technology hasn't been road proven. Show me a large number of these with over a 100K real-world miles, and I may then consider it. I was surprized that the Pilot was pretty agile. It moved quickly, plenty of power. One draw back, especially living here in the heat belt, only one AC compressor. That cabin has a lot of room and I wonder how long it will take to cool all that interior down.
I did get inside a new Accord. SAH-WEEEEET. Lots of room when compared to the 6th generations. The stereo absolutely, pure and simply, ROCKS. Like the satellite radio too. Did notice that the engine compartment was smaller than the 6th gen's. Don't know how a mechanic will get in there and replace the timing belt because there is absolutely no room to even put a breaker bar in there to pop the crankshaft nut off. Really really tight. Oil cap did say 5W-20......FWIW.

 

[Dad2leia]

Sounds like an annoyance. I just started really enjoy the i-VTEC smoothness and personality change in our '04 CR-V, but this sounds like a big step backwards. I realize the principal is probably fuel savings related, but couldn't this be done a better way?

 

[Matt_S]

I'm very surprised that Honda would release a variable-cylinder system that's even slightly detectable. Every review I've read about GM's and Chrysler's systems on their V8 engines states the transition was unnoticable. I would expect Honda, of all companies, to at least match that.

 

[yugrus]

I was always wondering about this technology. Does it not cool down cylinders in disabled bank to the point of spark fouling?..

 

[Matt_S]

quote:

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I was always wondering about this technology. Does it not cool down cylinders in disabled bank to the point of spark fouling?..

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I can't speak for Honda's system, but with GM and Chrysler, one cylinder at at time is deactivated and it's not the same cylinder all the time. So, basically, all the cylinders are still firing, but certain ones are skipped.

As for Honda's system, I doubt that fouling would be much of a concern. The operating cylinders will still produce heat which will be circulated to the non-operating cylinders via the coolant. When the non-operating bank is activated, it should come up to temperature very quickly. Besides, I'm sure Honda corrected the fuel maps for this condition so that cylinders aren't running rich after reactivation.

 

[merlin64]

The Honda system always shuts off the same bank, it is the rear bank near the firewall. I don't think you would get much cool down, my experience has been the engine switches between modes so much any cool down is minimal. Also, as mentioned the same hot coolant is circulating throughout the engine.

Look, the jury is still out on these systems. Yes, they work, computer technology has made the systems feasable. I still don't like it from a drivability point, but admittedly if you are not tuned in to engine function you won't care. Based on how many people are yapping on cell phones, most won't notice.

My concern is long-term reliability. Is there an effect from having one set of cylinders having 150k miles on them and another set that has the same milage but has been "freewheeling" for 50k out of the 150k? Will the injectors on the always-active side wear more than the other, and if so what will the effects be? Ditto the valves, will they recede more into the seats than the valves on the partial-run side? Will the compression become different between the banks and will this affect idle?

I plan on keeping my wife's van for a long time, so for better or worse I will probably find out.

 

[Schmoe]

Other good points that I had not considered by Merlin64. Think we'll just stick with the Accord for now.

 

[yugrus]

^ This, and what about cruising for 100 miles at the speed limit? It sounds like the shut down cylinders' internals will cool down to the point just above the coolant temperature, not exactly the normal operational conditions. Yes, they will heat up quickly upon activation, but still... And what about the oil getting into combustion chambers past rings? The clearances will not be as tight as in working cylinders, so the oil has a chance of accumulation on top of pistons. Will it burn off at once upon activation? Risk of excessive deposits?
I'm sure engineers have taken care of all that, but still I like GM & DC systems better.

 

[Dad2leia]

I also can agree that I don't like the fact that it is the same bank of cylinders shutting down. You would think that if the Honda engineers could come up with this system in the first place, they could have the computer alternate the cylinder banks that shut down, unless it is a closed loop type program (meaning can't switch around so to speak).

All of the other points, such as wear and tear, build up related and such, I also agree with. Maybe this technology could be the wave of the future, but the jury's still out on this one in my mind...

 

[Dad2leia]

I also can agree that I don't like the fact that it is the same bank of cylinders shutting down. You would think that if the Honda engineers could come up with this system in the first place, they could have the computer alternate the cylinder banks that shut down, unless it is a closed loop type program (meaning can't switch around so to speak).

All of the other points, such as wear and tear, build up related and such, I also agree with. Maybe this technology could be the wave of the future, but the jury's still out on this one in my mind...

 

[Titan]

We get 27-30 mpg on our VCM Odyssey, and once got 33.1 when we kept it under 65 on the HWY. Get 22-23 in town. If you step on it, there is no hesitation. In fact, it is very hard to detect it switching back and forth between 3 and 6 cylinders. I'm betting the Honda engineers have it down a lot better than the GM guys did their first go-round. If I'm wrong, I'm wrong, but, I'm a member of the jury, not just a bystander. I really like being able to get such good mileage out of a 4600 lb brick.

 

[Titan]

Oh, about the one bank of cylinders getting more wear than the other....I don't buy it. The reason is that the system won't run on 3 cylinders unless there is a light load of power required...so, those three cylinders that are doing "work" aren't working very hard at that point...at least, not compared to what they are capable of doing when the iVTEC system asks them to pound out some real power. Therefore, I don't sweat the "difference in wear" thing.

 

[merlin64]

My wife has the 3.5 VCM engine on her Odyessy van. Personally, I don't like it, you can detect the transition and it is constantly shifting from 6cyl to 3cyl mode. It feels like a second, big AC compressor kicking on and off.

I didn't want it but it comes with leather which she insisted on. Sadly, Honda does not give you a choice.

 

[Schmoe]

But there will be a "difference." As long as those cylinders are moving, whether powered or free wheeling, there is going to be friction. Didn't think about the oil on top of cylinders before, but makes sense. With the valves closed, oil is going to be drawn up the cylinder walls and eventually into the piston crown or head. I would suspect you'd see lots of carbon buildup on the closed bank side. Lot's of questions out on these engines. Will have to wait and see what type of real world problems emerge. Nothing is perfect...