2008 Honda Accord: "VCM" Cylinder Deactivation

I've had my Accord V6 coupe for about three weeks and rarely, maybe twice since I've had it, have I noticed the VCM in use. The ECO light appears often, which is ussually the only alert. I would describe it as subtle although, I've never driven the Oddyssey, Tahoe or any other vehicle with VCM to compare it to. I'm interested in seeing how much it helps in the real world though, as I have heard it comes at the sacrifice of performance.

I know it would bug the heck out of me if I could in any way perceive the engine cycling through its multiple personalities. This isn't the first account I've read that suggests that Honda's claim that this system is imperceptible to the driver may be less than accurate.
  
Question - are the EPA numbers for this Accord significantly better than those for the V6 Camry / Altima / Sonata? And are they significantly better than those for the V6 Accord coupe with the 6 sp. manual (and no VCM)?
  
Jaeger

I have to agree with Edmunds regarding the Odysseys VCM as our 05 Touring is very smooth in transition. If im not looking for the Eco light I dont know its working.
  
VCMI is a bit smoother in its transition and only allows the 6/3.
VCMII allows the switch from 6/4/3 and according to Edmunds its not as smooth.
  
Im actually a bit dissapointed in the system as you would expect at least slightly better fuel milage than the immediate competition (Toyota Camry V6) WITHOUT the loss in performance. In case you didnt know the VCM deletes the performance benefits of the VTEC system. This is the reason for the vast difference in power under the curve in the VCM V6 vs non VCM V6.
  
They make the same PEAK power (268hp) and PEAK torque (248lbft) but under the curve the non VCM V6 kicks the VCM V6s ass! I believe in the midrange the VCM V6 has about 30lbft less torque than the non VCM V6. The dyno has shown the non VCM 6MT coupe puts down around 240hp to the wheels with an ample amount of torque. The VCM V6 5AT put around 217 and less torque than the non VCM V6 6MT. Some of the "power loss" can be put on the automatic tranny, the rest is the VCM. The 6 speed manual has closer ratios than the 5AT.
 
EPA estimates for the VCM V6 5AT: 19/29 combined 22
EPA estimates fot the non VCM V6 MT:17/25 combined 20

I wonder if this may be the pattern for all the V6s. The 3.9 with the cylinder deactivation was down on horsepower, 233 versus 240.
 
The V8 don't seem to suffer from any horsepower loss.
 
The Accord loses some midrange torque it looks like. I never actually felt the system switch when driving the Avalanche, but I only drove it about 20 miles.
 
I think the biggest problem for all the systems is that they have to be instantaneous in response, otherwise can you imagine the lawsuits if the car stayed in 3/4 cylinder mode when trying to pass on a hill? Therefore, the manufacturers are really cautious when deactivating the cylinders.

I would be very nice to see a "lock-in" botton that would allow for continual 4 cylinder cruising. The remaning two cylinders could be activated at will when more power was wanted/requiered.

Hondacura -
 
I have to agree with you. I'm an 06 Civic SI owner, and I've let my dissapointment in this Honda engine be known and have felt the wrath of a few Accord owners online (though most tend to agree with me...echoing your sentiment).
 
The new V6 Accord shows very little true advancement in engine technology in my opinion, in both VCM and No-VCM models. It is substantially larger than the previous, class-leading, 3.0 v6. Therefore, it's made the Accord more nose heavy. It drinks more gas at idle.
 
Yet at the same time, in VCM format it does not give a competitive power advantage over anyone. I don't believe it's even competitive, power-wise, against it's previous iteration (the 3.0 liter from 2003-2007).
 
In Non-VCM format, the engine is equivalent to the current Altima 3.5 in powerband and fuel economy. And, of course, this version is only available on the coupe. Honda comes out with an engine one model year later than Nissan, and it is only "equivalent" to it in power and fuel economy. Since when is that normal?
 
In VCM format, the 3.5 liter engine produces less power under the curve than it's modern-day competitors. In layman's terms, in everyday driving this car is less powerful than the Nissan Altima 3.5 and the Toyota Camry 3.5. When you put your foot on the gas, your acceleration is not as strong in everyday driving. This is specifically due to the VCM. (i.e. the Non VCM version is as-strong, or near enough not to make a significant difference). And yet it's fuel economy ratings are not truly better than the Camry's, whose power is more prominent in day-to-day driving.
 
Again, this Honda engine came out over 1 model year later than the Camry's. Meaning they have additional development time.
 
Why do I say the Accord does not have truly substantial fuel economy differences? Because it is rated at 19/29 and the Camry is rated at 19/28; however, their combined ratings (I.e. regular driving) is both at 22.
 
So for those pure highway trips, you'll get ~1mpg better. In everyday driving, it's a wash.
 
Why is this a big deal? Well, if you buy a V6 it's probably for the everyday power. In many real ways, the V6 powertrain in the Camry is now more advanced than that in the Accord. It provides more real world power with equivalent fuel economy.
 
Why is this a big deal? Well, since when has the Toyota Camry ever had a more powerful and equivalent fuel economy engine to the Accord? Honda is known for their engines and powertrains, yet they have fallen behind.
 
The interior of these cars are where the difference is made, in my eyes. The Accord is an incredibly nice interior, in tan or black, while the Camry (at least in tan) is spacious yet cheap feeling.
 
Honda desperately needs to advance it's VCM to provide more real-world fuel economy benefits (it's a great technology in my eyes) while at the same time providing at minimum class-standard power. It needs a 6-speed transmission on it's V6 to advance this cause.
 
I look forward to seeing Edmund's reports, but it will be interesting to note fuel economy. Edmunds tends to do alot of road trips with their cars, where I expect to see 28-30mpg averages. But what will the day-to-day slog bring?
 
Joe
 
Fuel economy: I won't try and report on what too many owners are seeing, but from what I've seen so far and from EPA estimates

If the transition between 3/4 cylinder mode and full power is really seamless and instantaneous, shouldn't the engine go into 3 cylinder mode every time the throttle is lifted? Why power all 6 cylinders while idling at a stoplight?
 
FWIW, older Saab 9-5's had an asymmetrical turbocharger - powered by exhaust from all 6 cylinders, but boost was only fed to one bank (3 cylinders). This engine had major durability issues (primarily, catastrophic timing chain failures) and was discontinued in the 9-5. I don't know if the asymmetrical power arrangement contributed to the problems, but I wonder if VCM puts similar stresses on engine components.

Do the engine controls cycle which are the designated "off" cyclinders and which are the designated "on" cylinders to ensure more even wear?
  
I'm not excited about this VCM being required on V6 autos. Would really like to see a VCM-delete option, so we can let Honda keep tinkering for a few more years.

VCM is NOT an acronym, it's an abbrevation. You can 'say' acronyms, whereas with abbreviations you say each letter. I'm not a grammar Nazi but I'm sick of seeing this mistake made everywhere.

Definition of acronym: A word formed from the initial letters of a name, such as WAC for Women's Army Corps, or by combining initial letters or parts of a series of words, such as radar for radio detecting and ranging.
 
So yes, Variable Cylinder Management is actually an acronym. FBI is an Acronym. TLA is an acronym (if you don't know what TLA stands for, you don't work in the corporate world...)...
 
An abbreviation is a shortened word or name. Joe is really an abbreviation for Joseph (in my instance).
 
Regarding some others questions....I think it's a great point. To my knowledge, VCM only deactivates specific cylinders and does not vary the cylinders deactivated. It could not vary much, as it needs to remain as harmonically balanced as possible.
 
I could be wrong about that. I just haven't read otherwise.
 
Joe

Chris and Joe,
 
VCM is not only an acronym, but an abbreviation AND an initialism!
 
-mike

Joefrompa,
  I also miss the 3.0 liter V6, it was a great engine that was well matched to the Accord. It annoys me to watch cars get bigger and heavier when I found nothing wrong with the Accord's old size.
 
The three mode VCM deactivates the rear bank of cylinders (1-3), and the four cylinder mode deactivates cylinders 3 and 4. A crudely drawn picture:
 
              Cabin
         1 2 3
         4 5 6
          Front of Car
I also thought of the uneven wear issues from this, but if you think about it, if the excess vibrations don't cause any increased wear, you'll actually get better cylinder life on the ones that shut down. However, who knows if issues similar to the Saab 9-5 flipb mentions might crop up years down the road.
 
On another note, if you get the chance, I'd pick up the Accord brochure just for the nifty illustrations they have of the engine alone (it might also be on Honda's website). That is where I got this info.

Edmunds should chart the mileage, then compare it to their last V6 Accord sans that acronym. Abbreviation. Initiliasm.
 
Whatever. VCM. :-)

I prefer the term Phonetic Symbolism.
 
I applaud cylinder deactivation for it's simplicity, but in fact, the engine is actually less efficient (still moving the same mass but only half of it works). I would suggest running a leaner mix as less power is needed. That way all parts are still performing their function and you could actually decrease the displacement necessary.

estreka,
 
Great point about the mass of the engine under partial power. I guess the ultimate cylinder deactivation scheme would require a series of three V-Twin engines, coupled together with clutches between the crankshafts of each. That way, power can came from 2, 4, or 6 cylinders while the others actually shut off.

Joe I agree on all but one thing. The Honda 3.5 isnt any heavier than the 3.0L. I actually remember reading somewhere that the "new" 3.5 in the Accord is slightly lighter than the previous 3.0L.. Remember these engines are from the same basic 11 year old J series architecture and still smooth as butter. Enjoy!
 
(08 Accord EX-L V6 VCM 5AT sedan dyno video)
http://revver.com/watch/431630/tov-video-first-dyno-test-of-2008-accord-ex-l-v6/
 
(08 Accord EX-L V6 6MT coupe dyno video)
http://revver.com/watch/475758/tov-video-dynojet-test-of-2008-accord-v6-6mt/

"Do the engine controls cycle which are the designated "off" cyclinders and which are the designated "on" cylinders to ensure more even wear?"
 
Johnmarco, from my understanding the internals still actually move as they cant STOP so I dont see any problems involving uneven wear. The VTEC system actually closes the valves to the combustion chamber and cuts fuel/ignition to the designated cylinders....at least I think thats how the Honda system works.

hondaacura4
You are correct. My feeling about cylinder wear though comes from the fact that although it still is moving, there is no combustion occurring, and the piston is being driven by the connecting rod. I've simply assumed that the lack of combustion would lead to a decrease in cylinder wear. I readily admit that this theory is pure speculation though, so if anyone actually knows about this, speak up!

Jr - Usually the first thing to give out are the piston rings, which don't receive the majority of wear from the actual combustion, but rather from it's duty of keeping the piston from brushing against the cylinder wall. That won't be affected. The piston itself is pretty durable (in most applications) and less combustion will of course extend it's life, but it won't save you from a rebuild hundreds of thousands of miles down the road.

Regarding HondaAcura's earlier post about the VCM car being down on horsepower compared to the non vcm coupe - are you suggesting VCM was activating on a dyno run? I'd more readily believe that the slushbox would sap about 12% of midrange torque.
 
Does anyone here have actual knowledge of how the system is set up - are the cam profiles different, or do the lobes responsible for opening and closing the inactive valves uncouple hydraulically?

Tjbeck -
 
In honda's releases, they have stated that the VCM-modified 3.5 liter sacrifices low-and-mid range to have VCM compared to the NON-VCM 3.5 liter.
 
In other words, in the majority of your everyday traveling Honda has reduced the power output of this 3.5 liter to achieve it's rated fuel economy of 19/29.
 
I don't know that they "got rid of vtec" as someone else stated. But they did neuter the engine somewhat.
 
Joe

joefrompa,
the 29mpg corresponds to 70 or 75mph with the AC on based on the new EPA standards. At these conditions the VCM is in OFF position. So you cannot judge the effectiveness of the VCM system by that number. Also the average consumption is based on an average formula of the 29mpg (again with the VCM off) and the 19mpg city consumption (in which VCM is off most of the time)
So the average of these two numbers is not representative of the VCM system effectiveness because in daily driving the systme will be used more than it is used to derive the city, highway as well as the average EPA estimates.

Banhugh -
 
Well, if you are right, we should see some representative numbers coming from Edmunds in the near future.
 
Joe

joefrompa--
 
Ha! Not the way these Edmunds boys drive
 
: )

I agree that real-world fuel economy numbers are more meaningful that (even the new and supposedly more realistic) EPA numbers. Too bad Edmunds doesn't have a long-term 6sp. Accord Coupe on hand - which would give us the most meaningful information on VCM versus non-VCM in the same motor (and also 6 speeds versus only 5).
 
Still, the VCM Accord should do better mileage-wise than, say, the long-term Camry, right?
 
Jaeger

"I don't know that they "got rid of vtec" as someone else stated. But they did neuter the engine somewhat."
 
Joe, thats not what I meant. The VTEC is still there but its operates differently because of the VCM. It basically eliminates the performance enhancing mechanicals of the VTEC system. There are MANY variations of Hondas VTEC system. Not all versions are high performance oriented.
 
"I'd more readily believe that the slushbox would sap about 12% of midrange torque."
 
Tjbeck, very very true but the combination of the VCM, auto transmission and the ECM programming are all to blame. The sedan in the video was pretty fresh as it only had around 500 miles on it. No, the VCM wasnt operating during this dyno but the system itself is still present and still eliminates the high performance mechanicals of the VTEC system.

A little off topic, but has anyone dynoed the new VCM and non-VCM versions of the 2008 Odyssey?
 
Assuming the setup is similar to the Accord, this would be a way of measuring the VCMII performance degradation on two setups with the same transmission.
 
Of course, the valvetrains could be entirely different. But I'd think it would still give us an idea about the differences in the torque curve effected by VCMII.

To my knowledge there hasnt been any dyno tests of the Odyssey. Honda states that the non VCM Odyssey makes 244hp @ 5750 and 240lbft @ 5000 RPM and it of course uses the normal SOHC VTEC setup.
 
The VCM Odyssey has 241hp @ 5700 and 242lbft @ 4900. Honda claims to use i-VTEC on this engine, although its not the performance oriented i-VTEC found in engines like the Civic Si and TSX. The VCM2 systems seem to be pretty much the same in the Odyssey EX-L/Touring and the V6 Accord 5AT.
 
(Odyssey Non VCM Videos)
 
http://revver.com/watch/160722/tov-video-2006-onelap-honda-odyssey-overview/
 
http://revver.com/watch/163063/tov-video-2006-honda-one-lap-odysseys-part-2/
 
http://revver.com/watch/329684/tov-video-2007-honda-one-lap-odyssey-talladega-grand-prix/
 
http://revver.com/watch/329482/tov-video-2007-honda-one-lap-odyssey-talladega-grand-prix-pt-2/

The real question is what are the highway MPG improvements with VCM? If the gas mileage is not significantly better, then why complicate the operation of the engine and risk the problems that others have mentioned here? I tend to think that the four banger is probably better if your concern is mileage and a non-VCM V6 if simplicity and performance is more important. Or am I missing something here?

Anyone know how to reach any of these testers for a specific question? Thx.