Most people, including myself, say that the fuel economy drops by about 1-2 mpg. I think others that report no change, may have adjusted their driving habits unconsciously. The reason I say this is that when I was running without the VCMuzzler, there were certain parts of the road that because VCM was activated, the vehicle would slow perceptively and I would have to get on the gas to keep speed going up the incline. I would find myself anticipating this loss of power and accelerating out of VCM mode before I had to just to keep up with traffic. The ECU kicks out of VCM mode when you need to accelerate up a hill, but by the time it does, you're already scrubbed off speed and you have to get on the gas more to get back up to speed. EPA tests aren't real world, so some of these kinds of situations won't be emulated.I find it interesting that so many claim that disabling VCM caused no decrease in fuel economy, based purely on faith and anecdotal observation. So we are to believe Honda included this system which had no benefit whatsoever other than reliability risk, for what? A practical joke? And the EPAs higher mileage figures were... lies?
As I said, I think the majority of the people do report some loss in fuel economy, however, some of the changes in how the vehicle drives may change people's driving habits, which could account for a lesser drop. Not to mention, if your drive or driving habits do not lend to long stretches of cruising at constant speed, then you'll see very little difference in your fuel economy.
The pitfalls of VCM are well documented, and I'm not going to rehash them here. There were plenty of early problems, hence the lawsuit and all the warranty work and warranty extensions. Honda's "fix" of just engaging all the cylinders more frequently to prevent the bypassed oil that's pooled up in your cylinders to accumulate to the point that you get detonation and ring damage, doesn't sit well with me at all. You shouldn't have to do that if the system worked as well as they claimed. People are still getting excessive oil consumption with VCM, Honda just makes sure they burn it off more often.
This debate will never end, there will always be those that believe there's no way Honda would do something that's not in everyone's best interest. Fact remains that they save at least 80 million dollars a year by lowering their epa rating by 1 mpg, plus it's a selling feature to many people who don't know what it really does. Everyone is entitled to their opinion. I just prefer to look at evidence before I formulate my opinion, rather than just take Honda's word for it.