Sienna vs Odyssey

Wishful thinking there Dan, and unrealistic as well...what you suggest is impossible to do in any reasonably efficient way.

GM had the V8-6-4 engine in the 70's that did not have a stellar reputation for reliability. The current Chrysler Hemi engine has a multi-displacement engine. I'm guessing that it is shutting off the fuel injectors and ignition for the unneeded cylinders at highway cruise.

The Honda Accord Hybrid's V6 engine works the same way (3 cylinders shut down). However, I am skeptical that the increase in fuel economy from cylinder shutdown would be all that significant.

Various fuel-saving ideas certainly have diminishing returns to scale, and of course, there is the cost/benefit equation to consider. As the cost of fuel rises, various fuel-saving measures start to become more feasible. For example, shutting down half the cylinders might save 25% to 30% in fuel (as opposed to the 50% loss of output), but if gas is $3.50 or $5.00 per gallon, that fuel savings starts to become attractive and can still be more cost-efficient than hybrids.

I suppose it's possible but I wouldn't think that it's very efficient is it Ray?...I'd think that running 8 at 1/8 throttle(?) would be more efficient than running 4 at half throttle (or whatever's required) because an 8 cylinder engine is designed to operate 8 cylinders and it'd be horribly rough running if you actually SHUT OFF four of them.

Hell you can both feel and hear it when you lose ONE sparkplug, imagine losing FOUR!...

How do they get around the rough running HTM?

multi-displacement

Why would it be particularly rough running? Surely they're not going to shut unwanted cylinders down this way:

bang-bang-bang-skip-skip-skip

which would be pretty bad but, rather, this way:

bang-skip-bang-skip-bang-skip

??

I suppose the best way to know would be to test-drive and find out. Anyone done that?

Or get a review. I found this on Edmunds:

V6 engine also features a Variable Cylinder Management system (VCM) thatcan deactivate three of the engine's six cylinders during cruising anddeceleration with no impact to vehicle performance or passenger comfort.

DH's explanation is a very good one. Think about a crankshaft turning and power pulses being applied at even intervals along its rotation, kind of like lumberjacks on a log in the water. As long as the power pulses are applied with an even rhythm, the log spins freely. Get out of rhythm and things get out of balance.

Howdy,

No expert I, but...

In the situation you describe you still have compression, but no firing. I am quite certain that with the fuel saving systems that are being explored in this thread, there would be no compression in the cylinders that were not firing.

Otherwise, there would be an enormous waste of energy compressing the charge in those non-firing cylinders with each cycle.

All the best,

It's not clear how much loss there is if you do compress the air. To some extent, the compression of the air in the cylinder is sort of like a spring. Some energy is lost as heat but the compressed air in a non-firing cylinder will help to push the piston back after the top of the cycle has been reached.