Cylinder deactivation with MegaSquirt?

[fowljesse]

I was wondering if I could do this.
Under very low engine load, could I set it up so 1 or 2 cylinders doesn't get fuel, every rotation, especially changing which ones don't?

[RS_OBD'oh_2]

Ouch.

I'm guessing you're talking about the GM(?) style of running on less cyls to save on fuel. I don't believe that MS is advanced enough for this.. it's kinda the red headed step child of the standalone world. That being said, I don't know of any system that was built for this type of tuning. I'm also guessing you'd need to run a wideband for each cyl for the initial tuning process. Geez.. that more I think about this, the more problems I find that you'd need to overcome.
Sorry if I'm not much help, I do predict that if it can be done... you'd need many dyno hours and one hellova standalone.

[shameem]

I had a long discussion about this a while ago over at probetalk -
http://forums.probetalk.com/showthread.php?t=1701259140" onclick="window.open(this.href);return false;

The crux of the argument is to stop spraying fuel and "somehow" restrict the intake air...

[Nd4SpdSe]

Exactly, not until you can do sequential fire with the injectors and the motor has a function that leaves the valves open in the compression stroke so that compressing the air doesn't add an unnecessary load on the motor.

[onlytrueromeo]

I disagree with the idea of restricting air...there will still be compression/decompression that will cause there to be a loss of energy. The ONLY way this could work in my eyes would be to leave a valve open ENTIRELY for the cycle. The clear answer is intake valve of the two so that you screwing up the exhaust. This would cause problems w/o a custom intake manifold or ITBs. How would you do this without a "clutched" cam? Either way, this approach is silly.

Electronically controlled valves...AWESOME...practical? Not yet, unless you want to do the R&D (which would be ALOT)

Restricting air is silly...you need to do the opposite..unrestricted air to the off cylinders! ITBS or a custom intake manifold is necessary!

Hmm...I have some serious ideas about this to make it work, but what cost? Couldnt tell yet. My ideas are VERY different than what I've read about this, or how most engines that utilize it work...I will keep silent until I can either prove or disprove them myself!

[shameem]

You dont quite need sequential injection - you "just" have to cut the +12v supply to the injectors that you need to close....

The commercial cylinder deactivation works by closing both valves shut - the "air" trapped inside is compressed and decompressed repeatedly - the theory is that it takes energy to compress and it gives the energy back during decompression - sorta like an air spring..... However air is compressible fluid and it doesnt give 100% back and thats why the benefits are low....

Unrestricted airflow is somewhat not possible in multi-cylinder engines without ITBs - if the airflow is unrestricted the cylinders would do something called charge robbing - the cylinders with free flow would "rob" the air/fuel mixture from another cylinder whose valves are just beginning to close during the intake stroke - there is a whole boatload of internal combustion thermodynamics and fluid mechanics theory that comes into play..... Not to mention the fact that airflow measurement (MAF/VAF/MAP) is averaged for all cylinders not individual cylinders....

Besides if it was that easy - everybody would have done it already

[onlytrueromeo]

Thats why I said custom intake manifold, where some sort of "actuator" would open and all air going into and out of the cylinder would be directed somewhere else...this is actually quite easy...I agree ITBs would be the best still.

If you can monitor AFR you can change a MAF/VAF rating in a standalone program. You are changing the air going in/out of the engine by isolating cylinders so the airflow will actually be decreased, which will correspond with a preset VAF/MAF value rating/setting...all possible with computers!

In all honestly, I think firing alternating cylinders is the best way, but not the most practical. You would need a way to open/close VERY fast just like normal valves work...an easier way would be to have a rotating system...3 cylinders fire normally for 30 seconds or x amount of cycles, then the other 3 do this. I think the hardest part would be balancing the engine for this...in which case, it might be best to increase the duration so that there are "shudders". Reason I say this is because I think you need to look at the 2 extremes: alternating cylinders or completely shutting cylinders down for a long amount of time.

Also, this would not be on an "automatic" basis...there would have to be a button to activate the system - takes out ALOT of engineering time, and by implementing a button you are getting rid of complaints about hesitation and problems that can arise with a system that "fluctuates" kinda like how bad auto trannys keep switching gears when youre goin up a hill.

[mazdags94]

I wonder if it would be easier to balance if the engine was a straight 6. I think that based on the information on this thread so far, seperate throttle bodies would be necessary for each cylinder, electronic throttle bodies at that. This way, air could be controlled by the right programming of the ECU, and air could be restricted/cut off from the cylinders that are to be deactivated.

A friend of mine keeps trying to get me to try motorcycle carbs on my V6.... he may just be nuts but he's also running a turbo'd BMW M3 custom built and self tuned.... but I think he's still nuts

[Nd4SpdSe]

A friend of mine keeps trying to get me to try motorcycle carbs on my V6.... he may just be nuts but he's also running a turbo'd BMW M3 custom built and self tuned.... but I think he's still nuts

You do realise that Individual Throttle Bodies, also know as Velocity Stacks, are fairly common and has been done a few times on a KL?

You dont quite need sequential injection - you "just" have to cut the +12v supply to the injectors that you need to close....

Yes and no. Since MS is batch fire, it would just be easier to not fire X injector for X Cylinder, rather having a secondary system that overrides the primary system and prevent X injector from firing, but ya, either way works

That an interesting idea about the decompression of the compressed air, never thought of that.


In the end, I just thing cylinder deactivation is just a marketing plow for fuel economy on inefficiently designed systems. I know my old boss's old Caddy did it if there was a cooling system failure, and I do like that idea. For fuel efficiency, I think it would be less efficient. Id your driving at say 55mph, you require X hp to keep the vehicle moving, pushing against the air. Regardless of how many cylinders are running, you'd need the same amount of HP output regardless, so you would either have all 6 working so hard, or you have 3 working twice as hard, taking in more fuel and air, to make the required HP....than you have the paracitic losses from the rest of the motor that's not working, like compressing the air, which doesn't give you 100% return. In the end, you have all 6 cyl's working at peak efficiency, cylinder deactivation shouldn't be necessary. I really dont know how cylinder deactivation would yeild gains that way to begin with.

BTW, apparently GM uses solenoids to deactivate the lifters on selected cylinders of a pushrod V-layout engine. (Wiki)

[marcdh]

You do realise that Individual Throttle Bodies, also know as Velocity Stacks, are fairly common and has been done a few times on a KL?

May I bring to the witness stand Mr Leo323, last post here:
viewtopic.php?f=15&t=53102&start=75

[Nd4SpdSe]

In the end, I just thing cylinder deactivation is just a marketing plow for fuel economy on inefficiently designed systems. I know my old boss's old Caddy did it if there was a cooling system failure, and I do like that idea. For fuel efficiency, I think it would be less efficient. Id your driving at say 55mph, you require X hp to keep the vehicle moving, pushing against the air. Regardless of how many cylinders are running, you'd need the same amount of HP output regardless, so you would either have all 6 working so hard, or you have 3 working twice as hard, taking in more fuel and air, to make the required HP....than you have the paracitic losses from the rest of the motor that's not working, like compressing the air, which doesn't give you 100% return. In the end, you have all 6 cyl's working at peak efficiency, cylinder deactivation shouldn't be necessary. I really dont know how cylinder deactivation would yeild gains that way to begin with.

Interesting....apparently that the cylinders not working hard enough are less efficient!

High-powered multi-cylinder internal combustion engines may be necessary to satisfy driver demands for quick acceleration and/or heavy towing capacity, but during daily use they are generally operated at power settings of less than 25%. For example, at freeway speeds, less than 40 hp (30 kW) are required to overcome aerodynamic drag, rolling friction, and to operate accessories such as air conditioning.

However, when a gasoline internal combustion engine is operating under less than full load, the effective compression ratio is much less than the measured compression ratio due to the throttle not being fully open at the cylinder getting less than a full charge. The pressure and temperature generated at combustion are therefore less than under full load, and the thermodynamic laws which apply to all heat engines dictate that the engine will then be operating at less than its maximum possible thermal efficiency.

Thus, a high-powered, large-displacement engine is highly inefficient and wasteful when being used for normal driving conditions- the vast majority of the time. This is the motivation for cylinder deactivation, to effectively spread the work load of the engine over fewer active cylinders which then operate under higher individual loads and therefore at higher efficiency

Man this is a good read! I could quote the whole article:
http://en.wikipedia.org/wiki/Active_Fuel_Management" onclick="window.open(this.href);return false;

[onlytrueromeo]

^Exactly. In my thermo classes we discussed how high performance engines can never get the same mileage that smaller "fuel efficient" ones can...this is because of the wasted air intake and large displacement.

I do not think that car companies are very intelligent when it comes to efficiency, nor do I think that every idea has been tried. No matter what you do with variable displacement, it will never equal a small 3 cylinder motor from the start, however you can certainly cut it down ALOT from where it is today. An "air spring" is a silly idea...locking a cylinder closed is like constantly applying the brake when your stepping on the gas. The only other solutions are to 1) prevent the piston from moving (not really possible on a conventional engine - rotarys on the other hand...yes that is a different story)
2) Prevent compression or vacuum creation - the only way to do this is to allow the piston to go its cycle without air restriction. It would just suck air in and blow it back out. Problems with this idea is that air still has friction when entering/leaving the cylinder and you do not want "increased velocity" like you would when atomizing fuel, rather you want "maximum volume" of exit and entrance so that the velocity will be as minimal as possible. So you have 2 ways to accomplish this on an engine - use the valves or create a secondary air release system. Using the valves means it can be done on almost any engine, but you are limited to intake valves only, which will increase the velocity of the air coming in and you will have frictional losses as there will be a partial vacuum being created every time the piston moves. The other way is to basically "cut the top off" of the cylinder so that there is nothing in the way, no frictional losses except the piston against the cylinder (minimal losses) This is what I mean by having a "secondary exit". I dont know how you would accomplish this without some MAJOR engine work...custom heads that allowed you to bypass the head completely? Basically there would be runners connect that allowed for vented air to escape...there would still be a velocity problem because of the length the air needs to travel but it would be less than by using the valves.

Either way, A custom manifold needs to be created to change airflow when cylinders are deactivated. I also stand by my idea of not having a system like this fire every other cycle. It makes things too complicated and there are just more things that need to happen in order for it to be in a happy medium. It would just be easier to completely shut down certain cylinders for an extended time.

One question - what would happen to piston rings if an engine were ran with "open heads" meaning you had some cylinders firing but others being vented to ambient air like I propose - since there is minimal stress on the engine, it shouldnt cause premature wear due to overload, but as the cylinders cooled, I'd imagine there would be more clearance (rings shrinking), effectively lowering the friction in the cylinder even further, correct?

[mazdags94]

You do realise that Individual Throttle Bodies, also know as Velocity Stacks, are fairly common and has been done a few times on a KL?

When he mentioned "carbs" it threw me off bc I was thinking EFI. I know velocity stacks do exist and I have seen them before, but my friend's terminology was different than mine. When I mentioned 'nuts', I meant that he is crazy with ideas but could prolly make them work bc he has the time, money, and knowledge.

Never saw these on KL before though! That's hot.

[gunmetalpgt]

I disagree with the idea of restricting air...there will still be compression/decompression that will cause there to be a loss of energy. The ONLY way this could work in my eyes would be to leave a valve open ENTIRELY for the cycle. The clear answer is intake valve of the two so that you screwing up the exhaust. This would cause problems w/o a custom intake manifold or ITBs. How would you do this without a "clutched" cam? Either way, this approach is silly.

Electronically controlled valves...AWESOME...practical? Not yet, unless you want to do the R&D (which would be ALOT)

Restricting air is silly...you need to do the opposite..unrestricted air to the off cylinders! ITBS or a custom intake manifold is necessary!

Hmm...I have some serious ideas about this to make it work, but what cost? Couldnt tell yet. My ideas are VERY different than what I've read about this, or how most engines that utilize it work...I will keep silent until I can either prove or disprove them myself!

Actually, it is more efficient to have the valves CLOSED for the entire cycle.

[RX8SE3P]

You gotta think of it in a simple way. The car uses most fuel when taking off. Once cruising, it uses hardly any fuel (3-7L/100 kms depending on uphill or downhill etc).

Deactivating cylinders whilst cruising is silly if you think about it. The car will use more petrol uphill because it has less power, each cylinder has to work harder to maintain momentum. This will why plenty of big V6 and V8s do very good highway fuel consumption (many big 6.0L V8s can get less than 10L/100kms when cruising). I have noticed that my girlfriend's 3.5L V6 Mitsubishi did better economy than some of the 4 cylinder cars I once owned because it was hardly working to maintain the speeds and it was not revving high due to a well tall gearbox.

To make a KLZE have better economy, you'd be better off using an electric motor to take off, then switch to the petrol engine once the car has been propelled forward. I think this is how most hybrids work, when taking off from a complete stop you use most fuel. But by using an electric motor to take off, you save lots of fuel.