We would need some way of switching off the valves from being opened at all during the cylinder shutdown so the air trapped inside would act like a spring and help negate the drag effect of just cutting out the fuel.

Shutting down valves wouldn't be easy and likely requires very complex engineering

 

here is article on how it works on GM Engines
http://www.sciam.com/article.cfm?id=...half-cylinders
If you shut down only injection i am pretty sure it wont save any fuel it might even consume more.

 

Unfortunately i never drive on the highway but would love to see this happen.

 

From an engineer's perspective: You HAVE to kill the valves to make the pumping losses drop out of the equation. They are too high to keep in. This is impossible with our motor in OE condition. GM has been doing this for some time but they have special pushrods and complex ECU code that determines torque required. The really hard part is getting smooth transition between the two modes... very detrimental to the motor if you don't get that correct. The code needs to know the torque needed in each millisecond of opperation so that it can determine whether it can use limited cylinders to acheive the torque necessary. The engine is most efficient at max load... whether that's all cylinders or only some of them. So the ECU has to know when it can load up the engine efficiently on only 3 cylinders or when it is better to load up 4 cylinders only partially. (ever notice that good MPG cars have small displacement? That's not only to limit fuel consumption due to less cubes, but also to keep the motor loaded up whenever possible) Good thinking though, its thought like this that produces better vehicles.

(One might also remember that we have a turbo application... All of these are applied to N/A apps. Reason being: tremendous exhaust gas pressures. This further complicates things. You couldn't simply shut down the valves, you would have to reprogram their opening and closing... now you're getting into electronically actuated valves... hello BMW)

Summary:
lol it's already a 4cyl... so lose some weight.

 

IT does seem from the outline that switching a cylinder off could possibly cause more problems than create amy gains in MPG. I know BMW used a system on a few of there engines where there was no 'throttle' and the amount of air allowed into the cylinders was governed by the amount of valve lift that was created. It apparently helped fuel consumption but i think they had afew too many problems with it breaking down so ditched it.
I know now that they are championing auto start, stop and direct high pressure injection so they can run alot leaner.
Perhaps we just need to channel efforts into leaner cruising performance. Pushing safe combustion temps to reduce fuel economy. We run boost at the limits so why not monitor EGTs more closely and see just how lean we can take it..?

My two peneth

 

look closer to home , mitsubishi have been doin just that for years ,, mivec md (modular displacement) cuts fuel and sparks to two cyls while on cruise or idle for a set period ,, also uses a system similar to mivec to control the off cyl valves while on md.

http://en.wikipedia.org/wiki/MIVEC

 

I don't think EGT's will help you with anything. The EGT's actually drop on the lean side of stoich. I'm cruising at 16.0:1 so my EGT's are colder than stock. At any rate I'm not noticing much fuel savings by cruising lean. You still need the energy from the fuel to go forward, I just use more throttle to maintain cruise when burning lean. Also, the iron block 4g63 is kinda not good at burning lean. They seem to misfire quicker than other cars when running lean. I'm not sure if its the low compression or poor heat management of an iron block.

 

As stated already timing is critical another factor is the fuel i presume might act as a sort of lubricant for the intake chamber. I dated a girl way back when that worked for a company that tried to do this during the 80's oil/gras ordeal and they stopped due to premature wear on the cylinders that were not firing and being fueled. I do not know the details other than my earlier presumptions and that I personally would not do it. While I will not be saving money I am hoping to burn e85 as soon as the station opens near me. Granted this is more for power than economy as it will actually cost more than gas but much less than race fuel.

 

It sounds like your describing something very similar to rotational idle.

Also the evo ecu already has something similar hidden away in there, back in the day my evo4 would drop into a limp home mode when we were playing with adding a unichip which would drop cyclinders.

 

Exactly. I'm surprised noone else remembers this?

 

My friend has an evo 5 with an evo 7 ecu fitted.

If he sticks to 70mph in 5th gear, the ecu will drop it onto 3 cylinders, due to a vibration from his gearbox at that rpm / speed.

It won't do it on boost, or at a lower / higher speed.

Does not do it with an evo 5 or 6 ecu fitted either.

 

I drove my car around briefly today on 3 cylinders. I don't think that switching to 3 cylinders to improve economy is going to work. Most obvious part of my experience is that it causes pretty strong vibrations in the motor. Even with rotating which cylinder gets shut off, I still think the vibration would be bad. What I also learned was that one cylinder not running is an air pump that messes up the fuel trims. Even if the valves were held open, I still think it would mess up the NB O2 sensor reading.

 

yeah AFR's would be majorly affected...

hrmm ok I guess I wont bother doing on more on this one...