Variable displacement?

[nikos]

Haha this is pretty left field, but just curious:

As the AU motor can shut down cylinders to prevent overheating, theoretically would it be possible to manually control this infrastructure? Just curious as fuel consumption could be greatly reduced on the highway... Perhaps some modding to the ecu could achieve this?

Cheers Nic

[bodes-sh]

i don't see why you couldn't, but i don't know if i'd like to just go and start shutting cylinders down, i would imagine it would greatly affect the balance of the engine, and i really don't think it would do it much good.....in saying that, i guess someone may have tried it, or be willing to try it

[FGII-XR6]

an easy way to experiment would be to alter the signal from the temp sensor this would make the ECU think there is an over temp situation and start shuting down cylinders without actually overheating the engine if this works you may be able to switch in a bank of resistors till you get the desired effect I for one would be interested in the outcome

[schuldiner]

yeah, sounds plausible, the new chryslers can automatically shut down cylinders onhighway driving right? maybe chrysler forums or something have the info on how its done.

[onfire]

But why would you want to?

[EvilChief]

Originally Posted by nikos

Haha this is pretty left field, but just curious:

As the AU motor can shut down cylinders to prevent overheating, theoretically would it be possible to manually control this infrastructure? Just curious as fuel consumption could be greatly reduced on the highway... Perhaps some modding to the ecu could achieve this?

Cheers Nic

cylinder shutdown to prevent overheating? shutting down cylidner would actually not help at all. Fuel in itself is used as a cooling agent, the leaner an engine runs, the hotter it gets. Hence fuel injection cycles increase as water tempereature and/or air intake charge temperatures increase.

Have a look into some of the fuel maps for aftermarket ecus that are around or if u r lucky enough have a look at factory maps, which have an injection phase increase by percentage dependant on air and fuel temperature (aka air temp / water temp correction maps). these correction maps also alter ignition timing, pulling it down.

AUs dont shut down cylinders to prevent overheating.

there are several stages which lead up to an overheating event in an AU:
1: thermo fans both run at full power
2: auto drops back a gear to increase revs and waterflow
3: fuel injection cycle increases
4: dash lights up like a chrismas tree

as for answereing you question of shutting down cylinder, in europe either jeep or audi have implemented cylidner shutdown on some of their V8 engines ... do a google

[EvilChief]

Originally Posted by onfire

But why would you want to?

one word: fuel-economy

[bodes-sh]

Originally Posted by EvilChief

cylinder shutdown to prevent overheating? shutting down cylidner would actually not help at all. Fuel in itself is used as a cooling agent, the leaner an engine runs, the hotter it gets. Hence fuel injection cycles increase as water tempereature and/or air intake charge temperatures increase.

Have a look into some of the fuel maps for aftermarket ecus that are around or if u r lucky enough have a look at factory maps, which have an injection phase increase by percentage dependant on air and fuel temperature (aka air temp / water temp correction maps). these correction maps also alter ignition timing, pulling it down.

AUs dont shut down cylinders to prevent overheating.

there are several stages which lead up to an overheating event in an AU:
1: thermo fans both run at full power
2: auto drops back a gear to increase revs and waterflow
3: fuel injection cycle increases
4: dash lights up like a chrismas tree

as for answereing you question of shutting down cylinder, in europe either jeep or audi have implemented cylidner shutdown on some of their V8 engines ... do a google

if that's the case, then why did ford promote this when they released the au? it would shut down cylinders one by one till you either got stuck somewhere or you turned the engine off and fixed the problem....in an effort to reduce the effects of overheating. as for the v8's that do it, i'm pretty sure it'll shut down 4 at once, and to be honest, i don't think that shutting down 2 or 3 cylinders would save that much fuel for the power you would lose anyway

[burnz]

Originally Posted by schuldiner

yeah, sounds plausible, the new chryslers can automatically shut down cylinders onhighway driving right? maybe chrysler forums or something have the info on how its done.

chrysler/chev youse D.O.D. displacment on demant
by shuting the fuel and opening the exhaust on the compression stroke.
while cycling the cylinder firing order

[nikos]

AUs dont shut down cylinders to prevent overheating.

Thats not what the manual says.

I'd be most worried about the effects of the resulting unbalanced cooling of the block, as the mode is only used for emergencies, and the manual says only drive to a place where you can fix the overheat problem, no further.

But why would you want to?

Save litres on highway!

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

[nikos]

i don't think that shutting down 2 or 3 cylinders would save that much fuel for the power you would lose anyway

Cylinder pressure, 1st parag

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

[EvilChief]

Originally Posted by bodes-sh

if that's the case, then why did ford promote this when they released the au? it would shut down cylinders one by one till you either got stuck somewhere or you turned the engine off and fixed the problem....in an effort to reduce the effects of overheating. as for the v8's that do it, i'm pretty sure it'll shut down 4 at once, and to be honest, i don't think that shutting down 2 or 3 cylinders would save that much fuel for the power you would lose anyway

as i previously mention fuel is used as a cooling agent in itself, however, if you shut down one cylinder at a time (no matter which) you would kill the overall balance of the engine. ever had your 6cyl misfire on one or two cylinders and feel how rough it runs?

please give me a printout of the manual where it says it shuts down cylinders.

[burnz]

well i remember the peter wherit doing ad's for ford, specificly menshioning
shutting cylinder's incase of overheating

[EvilChief]

through the scanners we use at work, we cant even shut down cylinders. we can shutdown the entire injection cycle all together, which stalls the engine. my AU manual doesnt mention anything about this and i havent found anything about it in the service manuals at work (thene again i never spefically looked for it). also how does it know which cylinders to shut down. it doesnt have temp sensors for individual cylinders.

other than fuel economy i cant see any benefit of ceising injection to individual cylinders.

[nikos]

please give me a printout of the manual where it says it shuts down cylinders.

AU1 manual, page 19 under "instrumentation", titled "fail safe cooling"

It says not to run for extended periods of time, just until safe to pull over. It may not even stop the injectors, maybe it just does the spark.

But maybe with some experiment work and ecu mods it could be feasible.

[T3man]

Originally Posted by EvilChief

as i previously mention fuel is used as a cooling agent in itself, however, if you shut down one cylinder at a time (no matter which) you would kill the overall balance of the engine. ever had your 6cyl misfire on one or two cylinders and feel how rough it runs?

please give me a printout of the manual where it says it shuts down cylinders.

So fuel is a cooling agent eh? Yeah maybe, but not if it is being ignited to produce power.

The AU sixes DO shut down cylinders if an overheat situation accurs. It shuts them in sequence, not just one particular cylinder, followed by another "ad infinitum" until there are none left firing. So initially it may shut just one cylinder over a number of cylces - if the overheating continues it may then shut two cylinders over a number of cycles. But what I'm saying is that it won't be the same cylinders - it will choose them in (I presume) in a pre-set sequence that has been programmed into the ECU. I don't know at what stage it says I give up and shuts down all cylinders but I would expect that three cylinders would be the limit. A six will actually run reasonably smoothly on three cylinders albeit with very much less power naturally.

But back to the first Q - if you disconnect each alternate plug wire in the firing order and take the car for a drive you will have a bit of an idea how smooth the engine will be and how much power it will loose. After doing this, if you are happy with the result then all you have to do is "switch off" three injectors to get the economy you are chasing - how you do that to an AU ECU is up to some electronics guru to tell you, but I know it could be done easily on the 4.1 litre EFI motors because they batch fired on two banks.

[robbo_yobbo]

I think your taking a backwards step in shutting down cylinders to save on fuel economy.

The reason more cylinders = more fuel usage, is because theres more moving parts, meaning more friction, meaning more wasted energy. if it werent for friction, you could have an unlimited number of cylinders and not use any more fuel from one car to the next to go the same distance at the same speed, regardless of the total displacement, providing everything else was constant.

Based on that, if you shutdown one or more cylinders, your not reducing the total friction, and therefore will not save any fuel.

Further more, I think you will find you'll actualy go backwards, in that you will still be compressing the air in the shutdown cylinders, but not have the burn to expand it again and provide the power to compensate for the loss.

Reduce heat indeed it will, (someone mentioned that the fuel was a heat reducer so it wouldnt work, but remember, no fuel = no burn = less heat. leaner only means hotter if theres a burn.)

The only way your going to save any fuel economy by shutting down cylinders is if you can stop the inlet and exhaust valves from opening, and stop the piston from moving, which on any of the cars we drive, is not even close to a possibility, the motor would need to be specialy designed for it, and would not work conventionaly at all.

[FGII-XR6]

Originally Posted by EvilChief

cylinder shutdown to prevent overheating? shutting down cylidner would actually not help at all. Fuel in itself is used as a cooling agent, the leaner an engine runs, the hotter it gets. Hence fuel injection cycles increase as water tempereature and/or air intake charge temperatures increase.

Have a look into some of the fuel maps for aftermarket ecus that are around or if u r lucky enough have a look at factory maps, which have an injection phase increase by percentage dependant on air and fuel temperature (aka air temp / water temp correction maps). these correction maps also alter ignition timing, pulling it down.

AUs dont shut down cylinders to prevent overheating.

there are several stages which lead up to an overheating event in an AU:
1: thermo fans both run at full power
2: auto drops back a gear to increase revs and waterflow
3: fuel injection cycle increases
4: dash lights up like a chrismas tree

as for answereing you question of shutting down cylinder, in europe either jeep or audi have implemented cylidner shutdown on some of their V8 engines ... do a google

it is a well known fact that ford use this method of preventing overheating (shuting down cylinders) and it has been proven to workthe reason being with less gylinders working thos cylinders are no longer producing heat from the combustion process some of the other things you mention also are part of the process though

[T3man]

Yes robbo that is exactly correct - you will only save fuel if you can release the compression in the cylinders that are shut down - you only have to open one valve (exhaust) to do this. However on perfectly flat road running, if three cylinders were shut down there would be less fuel used, but not 50% - the reason that you wouldn't save the entire 50% is because of the mass of rotating parts no longer contributing to powering the engine. I can see it would only work in this "perfectly flat road" situation.

[stiddy]

Limp home mode... it does shut down cylinders, ive had this happen to my car.. mind you it was a test to see if it actually does this.
Drained most of the water out of it and took it for a drive, next thing you know the car starts running rough but only after 3000rpm.
Cruising along it was smooth as but sink the boot in and it wasnt running on full 6 cylinders. The more longer I drove the the more it started to run rough.
Mate and I even let it idle while we pulled plug leads off to see if it was sparking on all cylinders which it wasnt. And there was alot of fuel vapour coming out of the exhaust.
Top it back up with coolant, and no problems what so ever, mind you the temp gauge never really went much above half way.

[nikos]

If both valves could be held shut then the "air spring" could be achieved, but this is obviously impossible on a single cam engine.

I wonder if the fuel saving due to increased cylinder pressure (due to more throttle) would overcome the load of dead cylinders on the compression stroke.

[nikos]

And there was alot of fuel vapour coming out of the exhaust.

It just cuts the spark then, I guess the unburnt fuel helps cool the cylinders

[burnz]

Originally Posted by nikos

If both valves could be held shut then the "air spring" could be achieved, but this is obviously impossible on a single cam engine.

I wonder if the fuel saving due to increased cylinder pressure (due to more throttle) would overcome the load of dead cylinders on the compression stroke.

that is exactly what the ls2 does

[robbo_yobbo]

I think you will find the following to be true.....
These figures are pureley example figures, Im not even going to attempt for them to be acurate, thier just to keep the numbers easy.

example a)...normal cruising....
an 8.0L (massive!) 8 cylinder car is cruising down the highway at 100km per hour.
To maintain speed, the car is on 1/2 throttle, compressing 1/2 a litre of air per cylinder per revolution (4L of compressed air all up) and 50millilitres of petrol per cylinder, per revolution (400mL total per revolution).

Now for arguments sake, lets say that for every 400mL's of fuel burned at an AFR of 1:10 it produces 1megajoul of power. any less than 1 megajoul results in the car decellerating.

The reason we need to burn this fuel to maintain speed is to do the following.....
overcome road/tyre friction
overcome driveline friction
recharge battery and run other electric items
overcome wind resistance
overcome friction on moving parts on the motor
we need to squeeze the air before we can burn it (true if we can get away with squeezing less air, we can save energy)

example B.....1 bank of cylinders shutdown on the same car cruising at the same speed.

To maintain speed with 1 bank of 4 cylinders shutdown, this is what would happen (even with the exhaust valve of the shutdown cylinders open)

First of all, if we could open the exhaust port during the compression stroke (which we cant on a falcon) we would save the energy it takes to compress the air on 4 cylinders.
But then we would loose that energy on the other cylinders. why?????........
Remember, to maintain 100km/h we need to produce 1 megajoul to overcome the resistance, or we need to reduce the resistance.
To produce that 1 megajoul, we could no longer run on half throttle with 1 bank not burning. we would need to open to full throttle which would mean that now the 4 running cylinders are compressing 1L of air each instead of .5L - the total compressed air is still 4L per cycle and the energy it takes to overcome this resistance is the same as in example a.
now we still need to keep our AFR at 10:1, so now instead of 50mL of fuel per cylinder its 100mL x4 for a total identical 400mL.

You can see here that we're not saving on fuel at all. all we do is make the other 4 cylinders work harder to do the same job, reduce the total available power, increase engine stress, increase heat in the running bank, wich would actualy result in a reduction of power, or an increas of fuel consumption to keep the RPM the same.

The only way to increase the economy by shutting down cylinders, is to stop all asociated moving parts from moving - therefore reducing the total resistance. Even doing this, your not going to be able to get an 8 cylinder car to run on 4 cylinders as economicaly as a 4cy because of the increased weight, so my point of view is that this avenue is to an extent like flogging a dead horse.

I know that sounded like a physics/chemistry lesson, but I figured that was the simplest way to put it. I hope it was easy to follow

[nikos]

that is exactly what the ls2 does

On one bank i assume?

[burnz]

so chev and chrysler have got it wrong then?
8% fuel saving indepandant quote.

[burnz]

Originally Posted by nikos

On one bank i assume?

no it alternates
http://en.wikipedia.org/wiki/Active_Fuel_Management
http://www.edmunds.com/advice/specia...1/article.html

[nikos]

I think you will find the following to be true.....
These figures are pureley example figures, Im not even going to attempt for them to be acurate, thier just to keep the numbers easy.

example a)...normal cruising....
an 8.0L (massive!) 8 cylinder car is cruising down the highway at 100km per hour.
To maintain speed, the car is on 1/2 throttle, compressing 1/2 a litre of air per cylinder per revolution (4L of compressed air all up) and 50millilitres of petrol per cylinder, per revolution (400mL total per revolution).

Now for arguments sake, lets say that for every 400mL's of fuel burned at an AFR of 1:10 it produces 1megajoul of power. any less than 1 megajoul results in the car decellerating.

The reason we need to burn this fuel to maintain speed is to do the following.....
overcome road/tyre friction
overcome driveline friction
recharge battery and run other electric items
overcome wind resistance
overcome friction on moving parts on the motor
we need to squeeze the air before we can burn it (true if we can get away with squeezing less air, we can save energy)

example B.....1 bank of cylinders shutdown on the same car cruising at the same speed.

To maintain speed with 1 bank of 4 cylinders shutdown, this is what would happen (even with the exhaust valve of the shutdown cylinders open)

First of all, if we could open the exhaust port during the compression stroke (which we cant on a falcon) we would save the energy it takes to compress the air on 4 cylinders.
But then we would loose that energy on the other cylinders. why?????........
Remember, to maintain 100km/h we need to produce 1 megajoul to overcome the resistance, or we need to reduce the resistance.
To produce that 1 megajoul, we could no longer run on half throttle with 1 bank not burning. we would need to open to full throttle which would mean that now the 4 running cylinders are compressing 1L of air each instead of .5L - the total compressed air is still 4L per cycle and the energy it takes to overcome this resistance is the same as in example a.
now we still need to keep our AFR at 10:1, so now instead of 50mL of fuel per cylinder its 100mL x4 for a total identical 400mL.

You can see here that we're not saving on fuel at all. all we do is make the other 4 cylinders work harder to do the same job, reduce the total available power, increase engine stress, increase heat in the running bank, wich would actualy result in a reduction of power, or an increas of fuel consumption to keep the RPM the same.

I know that sounded like a physics/chemistry lesson, but I figured that was the simplest way to put it. I hope it was easy to follow

Good analogy.

But the more open the throttle, the less the engine has to work to draw air (on big cubers anyway). So more throttle on less displacement WILL actually save a bit of fuel.

Imagine an identical AU with an itty 2.0 donk. Even though traveling at 100km/h requires the same amount of energy, the car with the 2.0 will use less juice (because of cylinder pressure).

But anyway, as we only have one cam and can't independantly control valves then I guess we can put this one to rest!

[robbo_yobbo]

You will find that any savings to be had, come from the reduced available power.

If the powers there, and you flog it, you can get from 0-100 in say 5 seconds, reduce the total displacement by 1/2 and now it takes 10 seconds to go from 0-100kmh, you still get to 100, but you get there slower. The reduced rate of acceleration is what requires less fuel.

Now if we think about this, we could just reduce the rate of acceleration when running on all 8 cylinders too for an increase in economy, but because the powers there available to us, it gets used, and as does the fuel. - test it out for yourself.
Runing at 1/2 throttle is very similar to running at full throttle with 1/2 the displacement

This is where the savings are to be had, as if the powers not there, the fuel cant be used!

[robbo_yobbo]

Originally Posted by nikos

Imagine an identical AU with an itty 2.0 donk. Even though traveling at 100km/h requires the same amount of energy, the car with the 2.0 will use less juice (because of cylinder pressure).

I can see how that could be interpereted, what you will find though is weather its drawing the air into 1 cylinder or 8 wont matter, if its drawing the same amount of air (which it will need to to maintain the same workload) it will take the same amount of energy to do so.

Its like 1 joul (to vacuum) multiplied by 8 cylinders or 8 jouls to vacuum the same air into 1 cylinder.

for a 2.0L as opposed to an 8.0L it just has to do 3 more cycles to get the same air in and rund at 4x the rpm to produce the same burn which results in the same total air vacuum energy loss

For economy to benefit from increased compression on the continuing cylinders, you realy need to alter timing and be running a higher octain fuel, now its possible to alter the timing with engine management when one bank shuts down, but its not likeley that anyones going to have 2 fuel tanks for 2 different fuel types on any car.

these are the real reasons a 2.0 litre motor will run more economicaly....
-they cant accelerate as hard, so go a little slower, and accordingly use less fuel to do so
-they weigh less
-There is less surface area of contacting parts for friction.

sorry to burst ya bubble. lol : but it was a good idea.