GM, Chrysler, Mercedes, Honda, and Toyota have all tried cylinder cutoff technology. I think a 300 would be a good test-bed for this technology.

Here are some links to stimulate this discussion:

http://www.sae.org/automag/techbriefs/01-2002/
http://100megsfree4.com/cadillac/cad1980/1981/CAD81.HTM
http://autos.yahoo.com/green_center-article_19/

I am interested in applying the 1981 Eaton technology, but there are a number of other topics related to variable displacement technology that will fit nicely into this thread.

 

it would be a nice idea but would require a pretty complex computer to drive it.

 

The main reason I found that they only used the 1981 Eaton system for ONE year was that the computer and other controls were not up to controlling the system smoothly. People that buy caddies expect smooth. The new systems do not anticipate having this problem because modern computers are so much more powerful.

On the other hand - I am thinking of a manual system that would let me go from six cylinders to three cylinders at the flip of a switch. I am thinking of a two-carb system with one carb for each end of the engine on a divided intake manifold. Just shut off the gas to one carb, keep running until it sputters, and than flip a second switch to disengage the valves on that half of the engine. I would set it up to be able to do either end of the engine.

I would use this when cruising empty out on the interstates in the "wide open spaces". In several different systems they talked about 10-20% increase in mpg. The parts I need are in wrecking yards in '81 Cadillacs.

 

interesting. I have often thought in my head about running half an engine on compressed air with an AC compressor-turned-air compressor being belt driven. With a mechanical secondaries carb feeding fuel only when needed. But being bored at work does that, lol.

 

It just occurred to me that I do not need to cut gasoline to the carb on the "idle" end of the engine - the fact that both intake & exhaust valves will remain closed will take care of shutting the flow of fuel off just as when the engine is shut off. The needles & seats in the carbs will have to be in good shape (neoprene tipped needles) as the pump will keep making pressure. This does make it a single switch to flip for each end of the engine.

I have read that the 1981 system had a sensor that switched everything on once the throttle was moved past a certain point for passing, etc. This system did try to share the chores around, but the modern Eaton system that uses the lifters to "cut out" cylinders will have (in a V-8) four cylinders with "normal" pairs of lifters and the other four will be the only ones that get "cut out".

 

I must admit I didn't take the time to check your links; but from what I've heard of MDS, I thought the idea was to have the valves open when those cylinders are not in use ? That way the motor isn't wasting energy fighting to compress or pull vacuum on the air in those cylinders ?

 

What your saying makes sense, seems those articles are saying the valves are closed though. I think the reason for the valves being closed, if the dead cylinders were pumping in air, no fuel, then when it pushed the same air into the exhaust system, the O2 sensor would get a false lean reading, make fuel/spark adjustment dang near impossible, unless the computer went into another mode in which this state was measured and understood and it could adjust accordingly, but that would require a wide band O2, as the narrow band knows lean or rich and it all pivots on stoich, not very accurate.

Maybe? Not really an issue for a carb set up using the same concept, like the ford 300, as its basically two three cylinder engines.

Id say if you literally split the intake manifold, dont forget to T a vacuum line to each for brakes/tranny function (if automatic).

Interesting topic.

 

Glad to have you "in the thread", but it is the other way around: it takes energy to move air - an example is an air compressor. If both intake & exhaust valves are kept closed, then the air is compressed (taking energy) and then most of the energy is returned as the piston goes down with that pressure on top of it.

There are two other "fine points", the first of which I learned from reading those links (hint):

Given that there is a small amount of leakage past the rings, the inactive cylinders tend toward a condition where the pressure at mid-stroke is near atmospheric. There is pressure at the top end of the stroke and vacuum at the bottom end. The net energy loss per stroke is still small, but the vacuum portion of the stroke is important because it helps get a little oil above the oil control ring to keep the wear normal.

The other point is that when you compress and expand any material there is a slight (or not so slight) loss of energy, or to be accurate, a conversion of mechanical energy into heat. The amount of "hysteresis" loss varies widely with the material. The technical definition of elasticity relates to the amount of loss. A perfectly elastic material returns all the energy each cycle.

(Countrary to "common sense", a rubber band is NOT a very good elastic material because it has large hysteresis. You do not notice this in every-day life, but in the WWII era a high-performance aircraft engine was originally designed with rubber motor-mounts - automotive style. During testing the vibration-induced hysteresis heating was enough to MELT the rubber. The solution was to go with steel springs and hydraulic dampers which are designed to stabilize the spring-mass system while rejecting the heat without destroying themselves.)

Compressing and decompressing air does involve some hysteresis losses, but they are not significantly greater than the friction losses of the rings on the cylinder wall. The heat going into the cooling system from the "idling" cylinders is much less than the active ones. These losses are part of the reason that the mpg gains claimed in these engines are only in the 10-20% range.

Numerous hobbiests converted their sixes to threes and eights to sixes during the WWII gas rationing. They did this by removing pushrods or lifters. (You can bet they all converted back in 1945!)

 

Interesting.

If im understanding 95van. The initial reason for thinking that the valves be open. Think in terms of a straw with water inside. You cap the straw, the water stays put. Now with a piston, valves shut, wouldnt it have a similar effect, as the gap between rings and walls has to displace that cylinders volume, or you get a vacuum, wouldnt that create something of a suction effect, in which the working cylinders have to overcome this resistance? I really have no idea, I couldnt understand half what you wrote. I look at things from the simplest perspecitve as possible and work my way out as I grasp things.


Maybe Im thinking the valves would close before the intake/power stroke, when they would close before the compression stroke, then allowing your theory of compressed air stored energy to be released on downward stroke, seems there is a need for perfect engine/computer/valve solenoid timing then huh? Still seems to be a certain inefficiency, as three cylinder have to over come compression of six, suppose at cruise speed or when this system is activated, its not as great an issue, with momentum and all. Must not matter, as stated, it works.

 

Let me try a simple version that (so far as I know) is a direct analog for an "idle" cylinder's situation.

Assume that you do not have to deal with any air at all. (Say, the bottom and top sides of the piston are completely open so any air moves freely without any resistance. Remember the word ASSUME.)

Now put the piston at mid-stroke and attach a spring that can be stretched when the piston moves down from the mid-point and compressed when the pistion moves above the mid-point. At different portions of the cycle the spring will place a force on the piston, either helping it during one part of the cycle or hindering it on another. Averaged over the entire cycle, the amount of helping and the amount of hindering exactly balance. Because the spring returns all the energy it takes to compress or stretch it, there would be no loss at all, other than friction losses from dragging the rings up and down.

With air, there is a small hysteresis loss, but not much, so basically the non-working cylinders just go "along for the ride". The engine has pretty much the same mechanical losses running on three firing cylinders or six. The gain comes from letting the three working cylinders work harder, but in their efficiency range, with better mixture of gasses & so on.

 

I edited my last post a couple times, see if any of that makes sense.


I see what your saying but with air, even if you start mid cycle. Your gonna get resistance from mid point to top (compression), then some returned force or energy, top to mid point. Then mid point to bottom, again, your gonna have resistance, as it draws the piston from the cylinder, bottom to mid point, there will be no returned energy, as there was no compression taken place.

Something else I see, is you will have compression take place twice, which I interpret as resistance. On a normal four stroke, youd have resistance on the compression stroke only. With the valves permanently shut, you would have resistance on the compressinon and exhaust stroke.

I think your saying there will be a cool and high pressure area, but again, im not sure where this is going to come from, as its a dead cylinder?

How does your mention of expanding material, apply to the cylinder/piston/rings?

I might catch on eventually.

 

Maybe some of the confusion is related to this:

Both intake and exhaust valves in the "idled" cylinders are left continuously closed for the duration of the time that the engine is a three-cylinder. The spark plug is left firing, but would only finish igniting something for the first cycle. From then on a small amount of heat would be generated by ring friction and the heat generated by compressing and decompressing the air.

"Your gonna get resistance from mid point to top (compression), then some returned force or energy, top to mid point." YES, you are correct!

"Then mid point to bottom, again, your gonna have resistance, as it draws the piston from the cylinder, bottom to mid point, there will be no returned energy, as there was no compression taken place." NO - - From mid-stroke down, the pressure goes from zero to a partial vacuum. This means that there would be a force resisting the pistons motion. Then, when the piston moves from BDC to the mid-stroke position, there would be the same upward force, but it would now be helping the piston move and hence, returning the energy back to the system.

Trust me this does actually work out, whether approached the way we are discussing it, or analyzed by applying engineering and math. I do not mean to dismiss your questions. As a retired teacher, I have huge amounts of patience and I would not be discussing this unless I wanted to help explain these concepts, so keep asking questions.

 

Gotchya, I was 3/4 on the same page.


I understood the mid to bottom resistance, suction or vacuum, but overlooked the pull on the return movement...gotchya.


I understand it works, Im just trying to understand the inefficiencies/process, find the topic interesting, just not something Ive thought about till today.


Makes sense that mid point is when the lifter solenoid is activated.

 

Hell man, with your background, you should forget the carb setup, go straight for the megasquirt, control that bad boy efi style, you should be able to figure out a means to activate and deactivate injectors. Might be as simple (relatively speaking) as something along the lines of how cruise control works...have your DOD system become active once you reach a pre determined rpm for say 55 or 65 mph, and only if this predetermined rpm is maintained for a given number of seconds, that way it doesnt kick on everytime you drive at low speeds with low engine load, or when you hit the passing gear or revup to switch gears...whos knows...Im guessing.

 

I am "too old a dog to learn new tricks". Actually I might someday go to more modern technology, but I enjoy doing new things with the old techology more. On an EFI, cutting out the three cylinders that do not have the O2 sensor would probably work if the three "idle" cylinders' injectors were cut out at the same time. This way the loop would be closed around the working half of the engine. (Feel free to tell me why this would not work - I have little detailed experience with EFI, although I did replace a crank in a Ford 3.8 once. I was amazed that I got it all back together successfully.) (If the computer was smart enough to miss the electical load of the injectors, you could use a SPDT switch to switch in three resistors to keep the "brain" happy.)

I am bidding on an Offenhauser DP intake manifold on eBay. If I ever try this variable displacement concept on my 300 (not yet even in my truck), I would divide it in the middle so that the two halves of the engine each had a primary and a secondary.

P.S.: It doesn't matter what the stroke of the cycle is when the valves are left closed. After even a few seconds, there have been hundreds of stokes and ring leakage averages out the pressure so the mid-way point is atmospheric pressure.