I was just thinking that turning off 2 cylinders of a 6 cylinder when driving on the highway would be a great way to acheive a 34% reduction in fuel usage, or even 2 out of 4 cylinders and get 50% better gas mileage? What are the cons to rigging something up like this? I know a couple of the bigger engines (was it the hemi?) that does that to get better numbers? what have they done to the engine? or if you wanted to drive around on 4 cylinders until you needed to haul then turn it back to a 6 cylinder???? What would that entail? Would it cause damage>? I mean you obviously would have to do the opossing cylinders a V6 to make sure you didnt whack the crankshaft out of balance, but anything else?
Why dont more cars turn off cylinders when cruising on the highway
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You don't get near that amount of savings.
Or, you could shut off all 6 and get a 100% savings
The reason you don't get a real big savings is that the other cylinders have to work harder to take up the load of the dead cylinders. You can save almost as much, maybe more by adding another super overdrive gear to the tranmission.
Caddilac had a poorly executed 4-6-8 V8 about 1981 that ran on 4, 6 or 8 cylinders.
I would not think it is possible to do it aftermarket. I know Some GM trucks and now Dodge Hemi's have this feature on V-8 engines, but nothing smaller. It basicaly shuts down 1/2 the cylinders (turns off the fuel to them from what I understand)) when cruising on the highway and instantly turns them back on when needed. Is is supposed to give a v-8 the mileage of a v-6 on the highway. No real difference around town though.
MB. BMW, and others are going toward 6 and 7 speed auto transmissions to get better MPG.
I would trust cylinder deactivation in the long run.
I would trust cylinder deactivation in the long run.
Yeah, it is somewhat gimmicky (and likely an attempt to make V8 buyers feel better). And Honda seems to support the gimmick feeling by only using it on certain upscale models of the Odyssey minivan. If it works, why not use it on all V6s across the range? To get it to work effectively, you need to be able to close the combustion chamber to minimize pumping losses. IIRC, the current Northstar V8 also shuts down some cylinders, but cycles through them, as opposed to shutting down a whole bank. Not sure about that....
Right, taller gearing (or slower speed) is a much better way to save gas.
Right, taller gearing (or slower speed) is a much better way to save gas.
The process opens the valves to reduce throttle plate pumping losses. Killing the spark and fuel is the easy half of the story.
Throttle plate pumping losses are the bane of gasoline powered equipment. There's a recent article on this board about a new honda engine that hangs a valve open an extra amount of time, sometimes, to alleviate the problem.
Diesels have no throttle plates, denser fuel (BTUs per gallon), other benefits, and get probably 20-30% better miles per gallon than comparable gas powered stuff (VW being the only current example). So they're sort of the upper limit target for gas efficiency.
It's the same thing substituting a 1:2.73 final drive for a 1:3.50. You won't get 350 miles from a tank where you used to get 273. (3.5/2.73 better) But your MPG would be (theoretically) slightly better because you're lugging the motor more and opening the throttle more and lessening the pumping losses.
Throttle plate pumping losses are the bane of gasoline powered equipment. There's a recent article on this board about a new honda engine that hangs a valve open an extra amount of time, sometimes, to alleviate the problem.
Diesels have no throttle plates, denser fuel (BTUs per gallon), other benefits, and get probably 20-30% better miles per gallon than comparable gas powered stuff (VW being the only current example). So they're sort of the upper limit target for gas efficiency.
It's the same thing substituting a 1:2.73 final drive for a 1:3.50. You won't get 350 miles from a tank where you used to get 273. (3.5/2.73 better) But your MPG would be (theoretically) slightly better because you're lugging the motor more and opening the throttle more and lessening the pumping losses.
Are you sure it doesn't close the valves?
With all those engines in one body shell, there must not have been much room left for passengers.
No, but wouldn't that be nuts having the piston compress against closed valves (even though you get that power back when it goes back down)? Yes I know half the time a piston spends "going up" on a 4-cycle engine is pushing against closed valves.
I suppose it could find equilibrium either way... but would imagine less stress with the valves open.
Just read a story in the detriot news on the hemi truck with cylinder de activation,and the valves are both left closed(using the lifters oil supply)-it all happens it .0016 sec. or some such number.Compression bounces the piston back so its a wash or close to it.I assume the comp shuts off the fuel to,not somthing you could do after market
With the valves open you have all sorts of interesting problems with intake gases and exhaust gases from other cylinders getting mixed in. As you said, the bane of gas engines is pumping losses. Closed vales = zero pumping loses, only gas spring type losses as far as the air goes.
Suspicions confirmed
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Once they get pneumatic valve timing in production cars you'll probably see real gains in efficiency. With infinitely variable valve timing you can make a smaller displacement engine develop hp with higher rpms ...and turn it back into a Briggs and Straton fuel squeezer @ 70 mph.
So far it seems to work very well on the Chrysler Hemi powered vehicles.My neighbour has a black Dodge Magnum and got 24 mpg ,according to his trip computor,on his last run to Niagara Falls.Thats fantastic for a 5.7L engine!
Thanks guys, I had no idea thats why I asked! I have thought about changing the gearing in my tacoma to get better gas mileage but it would probably be a dog as far as acceleration goes. Love having a truck hate the gas mileage! Also I think the new Hybrid accord does shut some of the cylinders down? anyone know for sure? I was wondering if this was another way manuf may increase fuel efficiency in the future.
I'm too young to have experienced the Cadillac 4-6-8 engine, but I remember hearing about it. What was the problem with it anyway?
BTW, 24mpg out of a v8 powered car isn't that extraordinary. Lots of other v8 cars are in that mpg range without this trickery... right?
BTW, 24mpg out of a v8 powered car isn't that extraordinary. Lots of other v8 cars are in that mpg range without this trickery... right?
It was an all too common release of an engine for production by GM while it was still a Beta product.
The idea was OK and it but the execution was problamatic.
I remember a discussion I was involved in not too long ago with a user who I haven't seen post here in a long time about pumping losses. The whole thing that started it was my statement that:
EGR reduces pumping losses.
EGR reduces pumping losses.
It sure does take power to maintain high manifold vacuum during cruise conditions.
Like posted, cycling cylinders, or deactivating them, makes the remaining cylinders do the work, and the throttle is opened much more, with much less manifold vacuum to maintain.
Like posted, cycling cylinders, or deactivating them, makes the remaining cylinders do the work, and the throttle is opened much more, with much less manifold vacuum to maintain.
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