I’m considering buying a 2006 Honda Odyssey with variable cylinder management (VCM) and am wondering if VCM really does improve fuel economy and if so, what improvement could I expect?
Based on what I’ve read, don’t expect any earth shattering improvements. A 1-2 MPG improvement is the consenus.
The only real way to know whether it’ll save gas is to compare the EPA ratings. Many of these things are more marketing than actual savings, however if it’s what you want go for it.
I just looked at that when I saw an advertisement for it over the weekend. The Honda Pilot has the same system. The EPA estimates from 2 years ago when I last looked were 15/21…the current ones for this new system are 16/23. A difference…sure…But nothing real big here.
The main advantage of a four cylinder engine is its lower weight. The problem with VCM is it doesn’t decrease the weight of the engine, so fuel savings will be minimal.
It also doesn’t reduce reciprocating masses.
We had a long thread on this subject some time back. My own impression is that it’s more marketing hype than a technology advance.
“The EPA estimates from 2 years ago when I last looked were 15/21…the current ones for this new system are 16/23. A difference…sure…But nothing real big here.”
The highway mileage increased almost 10%. Not amazing, but a clear inprovement.
I agree, there are theoretical advantages, but the Toyota 3.5l non-VCM V6 consistently get better mileage than the Honda VCM 3.5l. and has the same power.
Also its really comparing two different varieties of apples. The 2009 is a redesign vs the vehicle of two years ago. I have a strong feeling power/torque is up slightly and weight too.
Not easy to compare the difference.
21/30 MPG for a 4-cyl 2009 Accord w/ auto
19/29 MPG for a 6-cyl 2009 Accord w/ auto
The 2008 6-cyl has the same estimates, but the 4-cyl is down 1 MPG on the highway.
The observation that the Toyota non-VCM engine gets better FE than the Honda VCM engine may prove that VCM doesn’t have any benefits, or maybe the Toyota’s variable valve timing matches the benefits of VCM.
Instead of cutting half the cylinders, retard the intake cam so that the intake valve doesn’t close until the piston is over half way up the cylinder and you effectively have cut the engine’s displacement in half.
Or maybe the Toyota has a taller overdrive and/or is a lighter, more aerodynamic vehicle.
VCM and varible valve timing are two different things. The Honda engine uses varible valve timing and VCM. Many cars have varible valve timing these days. I would even go so far as to say that more cars sold today have it than don’t.
The way I understand it, Honda’s V-TEC simply uses two different cam lobes to open the valves, one optimized for high rpm and the other optimized for low rpm.
Toyota’s VVTi changes the phasing of the intake cam. Advanced is good for low rpm torque at full throttle and retarded is good for high rpm, however, during idle and low throttle use, the cam is also retarded, maybe even more than what is optimum for high rpm power. In effect, the engine is being throttled with cam phasing to a large extent.
Honda’s i-VTEC is the same thing. So is BMW’s VANOS, Nisaan’s newer VQ engines use it, as do most 2005-up Subarus. Most VW’s and Audi’s have a version of Porsche’s Variocam Plus, which again is the same basic thing; camshaft phasing.
The way I understand it, Honda’s V-TEC simply uses two different cam lobes to open the valves, one optimized for high rpm and the other optimized for low rpm.
Honda’s V-TEC has a third position where the valves don’t open at all, like when you want engine compression to slow the car.