Variable displacement?

[nikos]

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!

That is 100% true, but an internal combustion engine is not that black & white. A thing called "pumping loss" is what you're overlooking. Its all in this article.

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

[nikos]

Sorry robbo missed ya last last post. GM seem to have it workin in their favour though, so it must work a bit.

[robbo_yobbo]

just had a read through the artical, seems to make sence, but I must say that Im a little more than skeptical on an 18% improvement in fuel economy - and doubt its compared with a farir comparison with no other variables.

ie. bench tested to run at the same RPM, accelerating at the same rate, decelerating at the same rate etc, as opposed to WOT untill it reaches a certain RPM in both modes (as the reduced displacement mode would take a bit longer to get to the same RPM and use less fuel in the process).

What there reffering to as "pumping loss" is in reality the restriction created by choking the throttle, and after reading it, could see how its possible to reduce some negligable amount of resistance there when shutting off cylinders, but I again think that that will be offset by the working cylinders being put under additional stress and having detrimental effects that balance out the positives.

I guess its something we'll find out more about in the future, but definiteley not a viable possibility on the falon motor as it is.

Must say though, it is an interesting topic

[nikos]

I think they say 8% not 18%. Aything that saves fuel is good, but as you say side effects will appear.

Hypothetically if two motors, one with DOD and one without, were put through idenitcal lives (hours, throttle position, revs etc), it would be interesting to see how long the DOD motor would last compared.

I guess it would wear more, due to the increased number of warm-up/cool-down cycles. Although on the contrary, less combustion in the chambers would surely prolong life.

I spose we'll have to wait to find out!

[burnz]

Originally Posted by nikos

I think they say 8% not 18%. Aything that saves fuel is good, but as you say side effects will appear.

Hypothetically if two motors, one with DOD and one without, were put through idenitcal lives (hours, throttle position, revs etc), it would be interesting to see how long the DOD motor would last compared.

I guess it would wear more, due to the increased number of warm-up/cool-down cycles. Although on the contrary, less combustion in the chambers would surely prolong life.

I spose we'll have to wait to find out!

well for the truck drivers out their the tecknowledgy is the same as a jake engine brake

[JC]

Interesting theories, but surely this should be in the pub/bar area - it's has nought to do with real life AUs.

[FGII-XR6]

Originally Posted by JC

Interesting theories, but surely this should be in the pub/bar area - it's has nought to do with real life AUs.

it think it belongs here it is about what is theoretically possible in an AU it would be an interesting experiment (not that i would actually do it myself) someone may want to do this if it is possible for day to day use and switch it off when you want grunt. As i said not my cup of tea but worth exploring. even though I wouldn't do it I would be interested to see how someone might go about it what dramas they have and how they solve them. I have already given a starting point for the experiments in an earlier post. so good luck all you inventors out there

[JC]

Theoretical discussions belong in the Pub. The AU section is about discussing and sharing our cars and helping with mods, and maintenance etc.

[FGII-XR6]

we'll ust have to agree to dissagree then

[JC]

Originally Posted by au3xr6

we'll ust have to agree to dissagree then

At least until a mod sees this and decides one way or the other.

[nikos]

it think it belongs here it is about what is theoretically possible in an AU it would be an interesting experiment (not that i would actually do it myself) someone may want to do this if it is possible for day to day use and switch it off when you want grunt. As i said not my cup of tea but worth exploring. even though I wouldn't do it I would be interested to see how someone might go about it what dramas they have and how they solve them. I have already given a starting point for the experiments in an earlier post. so good luck all you inventors out there

If you read above you'll find that we discovered its impossible to do on the AU motor.

This thread started off in the right place but has since become a pub thread.

[FGII-XR6]

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.

you could get the air spring to work on a single can it would be a matter of having either an electrical or hydraulic acctuator on the rocker arm when not activated it would cause the rocker to be too short to push the valve

[DJM83]

Originally Posted by nikos

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.

And as it says in there its only available on AU I6 engines not V8's incase anyone didnt know. But if people are worried about economy, buy a smaller car :

[Mechan1k]

Originally Posted by 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.

Also in an auto ... the EEC puts that into LHM as well ... locks it in 3rd.

Also EGAS doesn't have cylinder shut down .... just the auto goes into LHM ... temp still skyrockets though.

Been there done that ... not fun in Summer heading up hills around Sydney loaded up. Should have that sorted now ... twin core radiator :

[robbo_yobbo]

Originally Posted by au3xr6

you could get the air spring to work on a single can it would be a matter of having either an electrical or hydraulic acctuator on the rocker arm when not activated it would cause the rocker to be too short to push the valve

This would be extroadinarily difficult (and from an economic viewpoint - pure stupidity) to modify an existing au head to do this. but just so no-one goes out to try it by just doing the above only (not that I think anyone will due to the difficulty on its own)

you would need to.....
-kill the injector to the "dead" cylinder
-kill the spark so your not wasting the energy your attempting to save trying to ignite air
-either open the exhaust valve on the compression stroke, or close the intake valve on the intake stroke (possibly using the method in the above quote) to create what the wikipedia artical refers to as an "air spring"
-create a way to control the timing of it all.
-alternate the "dead" cylinders appropriateley so that your not causing the same cylinder/s to be continualy shutdown creating unecessary vibration or strain.

the length of time that the ignition, fuel and valve status is altered for would have to be very accurate and rpm dependent.

If it were me (which I can say it never will be) I would look at controling timing on injector pulses......ie....
assuming cylinders fired in the order 123456 on an I6 (which I know they dont)..... when the impulse is given to injector 1, power and ignition is killed to cylinder 2 and the valve status altered (sidenote -weather that be both valves closed or both valves open makes no real difference IMO, probably both valves closed woul save a miniscule amount of energy and prevent exhaust from going backwards into the plenum and being sucked into another cylinder so while not likeley may be the better option) injector, ignition and valve status of cylinder 2 remains altered untill cylinder 3 recieves an injector pulse and then injector 2 returns to normal operation for the next 2 cycles.

next kill cylinder 5 in the same method, then 3, then 6, then 4, then 1, and then repeat from the top AFTER cylinder 2 has fired normaly again so that your not killing 2 ajacent cylinders in a row - or something similar.
This method would see 4 opperational cylinders

or kill 246 on 1 cycle and 123 on the second for the next cycle

Now I havnt put any thought into this or paid attention to detail, and its likeley that the "dead" cylinders status would have to be killed before the preceeding injector fires, and would need to remain killed after the following injector fires, but you get the jist.
Point is, id idvise anyone not to even bother contemplating the idea!

Nothing is impossible, but it appears the only reason anyone would want to do this is to save money on fuel economy, but the cost and time involved with setup and exmerimentation would far outweigh any economic gains (if any) to be had. :togo:

[FGII-XR6]

True robbo I wasn't saying it is easy but I was just stating it was theoretically possible on a single cam engine to get an air spring effect in reality it would be a major engineering feat

[robbo_yobbo]

Originally Posted by au3xr6

True robbo I wasn't saying it is easy but I was just stating it was theoretically possible on a single cam engine to get an air spring effect in reality it would be a major engineering feat

I figured, I was just adding for the benifite of anyone who got exited and thought "I might go try that now" lol

[burnz]

Originally Posted by robbo_yobbo

or kill 246 on 1 cycle and 123 on the second for the next cycle:togo:

should't it be 153,
624.

[robbo_yobbo]

Originally Posted by burnz

should't it be 153,
624.

after re-reading, i actualy meant to type 246-135, but screwed it up in my haste.

but even still, I have no idea, so your probaly right, I was just giving random examples based on a firing sequence of 123456, the only point implied in my post was to alternate the shutdown cycle, and wasnt based on the actual firing sequence of the I6 (because I dont actualy know what actual the firing sequence is).

if however (based on 123456 firing sequence) you killed in the order 153-624, you would still only net 2 dead cylinders instead of the 3 obtained by a kill secuence of 135-246 because the following would happen....

if killing in the order of 153246
miss,2,3,4,miss,6,1,2,miss,4,5,6,1,miss,3,miss,5,m iss etc
this results in 6 misses over 18 intended fires (3 revolutions), which shutsdown a net of 2 cylinders per rev.

if killing in the order of 246-135
1,miss,3,miss,5,miss,miss,2,miss,4,miss,6 etc
this results in 6 miss's over 2 revolutions, netting 3 dead cylinders per rev.

If anyone is brave enough to attempt it themselves, and has enough time and money to throw away, the finer details like this are something you should already know anyway.

[burnz]

Originally Posted by robbo_yobbo

after re-reading, i actualy meant to type 246-135, but screwed it up in my haste.

but even still, I have no idea, so your probaly right, I was just giving random examples based on a firing sequence of 123456, the only point implied in my post was to alternate the shutdown cycle, and wasnt based on the actual firing sequence of the I6 (because I dont actualy know what actual the firing sequence is).

if however (based on 123456 firing sequence) you killed in the order 153-624, you would still only net 2 dead cylinders instead of the 3 obtained by a kill secuence of 135-246 because the following would happen....

if killing in the order of 153246
miss,2,3,4,miss,6,1,2,miss,4,5,6,1,miss,3,miss,5,m iss etc
this results in 6 misses over 18 intended fires (3 revolutions), which shutsdown a net of 2 cylinders per rev.

if killing in the order of 246-135
1,miss,3,miss,5,miss,miss,2,miss,4,miss,6 etc
this results in 6 miss's over 2 revolutions, netting 3 dead cylinders per rev.

If anyone is brave enough to attempt it themselves, and has enough time and money to throw away, the finer details like this are something you should already know anyway.

yeah i do understand
note a 4 cycle engine only fire's once every two rotation's

[robbo_yobbo]

picky picky, lol, but yeah, ^^^what he said^^^, this threads dead anyway, and nobodys gonna be dumb enough to try it.

[svo347]

Originally Posted by JC

At least until a mod sees this and decides one way or the other.

Looks like its been decided on hey.....

[outback_ute]

Sorry for jumping in late, but I think there could be a small economy gain to be had. I think it has been said the Failsafe Cooling cycles the cylinders that don't fire. Even though there would still be a compression stroke, a reasonable amount (less heat generated by the air being compressed) would be returned. As the cylinder shutdown cycles around the impact on the balance could be minimised so long as the sequencing was done correctly - I imagine the one Ford uses would be a good place to start.