Will DOD be a DUD?

[Cav]

OK so my post was a little bit tongue in cheek.
After all you can't have everything

[parawolf]

Originally Posted by merlin

Depends on your definition of "go". I don't think tractors or B-doubles have much "go" but they have plenty of torque. I'd rather have horsepower.

Ignore Tractors for a start, but take the engine section of a b-double (no trailer) Have you seen those things take off? They can smoke 'em up quite easily! Anyway... getting off topic here.

I really do believe that DOD will be a flash in the pan technology. People will realise that regardless, you still have a 6.0Litre V8 under the hood which must be fed petrol and air.

Whats the bet that DOD also only works after the engine is fully warmed and then some. So what 30 minutes after warm switch on? That means next to useless around the city or down to the shops.

[Sox]

Originally Posted by 4Vman

With all this talk about "DOD" being the new catch phrase or acronym of the trendy for Fuel economy im not at all convinced

I poo pooed DOD a while back whilst discussing the so called merits of it with 'ssbaby' on the old forums.

Im sure the car companies have done their homework

Whilst that may be true, many other (better) car companies have also done there homework, and don't use it.

however there are some points that concern me:
1) shutting off cylinders will create uneven heat production through the block, will this cause premature head gasket failure from warping?
2) will uneven heat distribution cause eratic expansion and contraction in the block causing uneven bore wear?

Possibly, however as some have said, it will likely cycle through different cylinders.
Even so, I remain very sceptical on the longevity of such a design.

3) If a car requires 100kw's to maintain a constant speed does it matter how many cylinders it uses to make that 100kw's? Remember fuel has a caloretic value thats constant. eg: more power needs more fuel.
4) is there a tangiable benifit from producing 100kw's from 4 cylinders V 8 given frictional losses will be almost the same?

Both good points.
The reduction in torque will require greater throttle openings to achieve the same result. Catch 22.

The early feedback im seeing from motors using this technology is there is very little gained in fuel economy in real world situations and the potential down sides as mentioned might be worse...

I personally see it as a huge gimmick, just marketing BS at it best.

If it was a good thing, BMW would have been using 10 years ago.

Rick.

[4Vman]

Originally Posted by Sox

I poo pooed DOD a while back whilst discussing the so called merits of it with 'ssbaby' on the old forums.

Whilst that may be true, many other (better) car companies have also done there homework, and don't use it.

Possibly, however as some have said, it will likely cycle through different cylinders.
Even so, I remain very sceptical on the longevity of such a design.

Both good points.
The reduction in torque will require greater throttle openings to achieve the same result. Catch 22.

I personally see it as a huge gimmick, just marketing BS at it best.

If it was a good thing, BMW would have been using 10 years ago.

Rick.

Thanks Rick,
so the vast majority of people seem to be able to put forward good rational reasons to suggest DOD is a marketing ****, ill be interested to see what the Darkside hangs their hat on with their new motors...!

[Steve D]

Originally Posted by Psycho Chicken

I can't see much of a point, the piston on the power stroke has to work twice as hard. You're still running compression strokes, which rob power. Unless there's some sort of VTEC type cam lobe that bleeds compression out the exhaust or something? Even still, friction would be high.

As I understand it, the 'inactive' cylinders act more like a spring. You've got to use energy to compress it, but you get that energy back on the expansion part of the stroke, so you're just left with friction losses only.

Originally Posted by 4Vman

If a car requires 100kw's to maintain a constant speed does it matter how many cylinders it uses to make that 100kw's? Remember fuel has a caloretic value thats constant. eg: more power needs more fuel.

I'd doubt you need that much power to maintain a constant speed. Most of the time, you're on part throttle and using only a small fraction of your engine's potential. The only times your engine's really working hard is under heavy acceleration, travelling near Vmax or during a dyno test.

[Sox]

Originally Posted by Steve D

As I understand it, the 'inactive' cylinders act more like a spring. You've got to use energy to compress it, but you get that energy back on the expansion part of the stroke, so you're just left with friction losses only.

How do you get the energy back if there is no combustion?
The must be some kind of valve deactivation for there to be no upstroke compression losses.

I'd doubt you need that much power to maintain a constant speed. Most of the time, you're on part throttle and using only a small fraction of your engine's potential. The only times your engine's really working hard is under heavy acceleration, travelling near Vmax or during a dyno test.

I suspect he used 100kw as an example, his reasoning still applies.

Rick.

[4Vman]

Originally Posted by Sox

How do you get the energy back if there is no combustion?
The must be some kind of valve deactivation for there to be no upstroke compression losses.

I suspect he used 100kw as an example, his reasoning still applies.

Rick.

Yes, spot on, it was a theoretical example.

[Dark Horse]

Surely with only half the cylinders at work at any one time, wouldn't the vibration coming from the engine be quite substantial?

I haven't experienced how DOD runs in cars, but we have V12 turbo diesel engines at work for marine applications and when they shut down 6 cylinders when idling and not in gear the vibration really gives the engine mounts a good workout.

[Steve D]

Form an Automotive Industries artcile (US trade mag):

Unlike GM’s system, which uses an add-on oiling plenum to fill the lifters, the Hemi’s hydraulic lifters are fed through oil passages machined into the block. With the use of Electronic Throttle Control and sophisticated algorithms the transition from four to eight cylinders can be done in 40 ms.

As for the second point, this would probably been a better quote to bounce off:

Originally Posted by 4.9 EF Futura

Hey you raise some great points there. i.e. have 8 cylinders making 100kw or 4 cylinders working twice as hard and using just as much fuel to make same power.

Getting 100kW out of, say, a 240kW V8 would probably require all cylinders to be working, but if only 50kW is necessary to maintain 100km/h, then it's less of an issue.

Mind you, I'd probably wait a while before buying one myself!

[Bossxr8]

Originally Posted by Dark Horse

Surely with only half the cylinders at work at any one time, wouldn't the vibration coming from the engine be quite substantial?

I haven't experienced how DOD runs in cars, but we have V12 turbo diesel engines at work for marine applications and when they shut down 6 cylinders when idling and not in gear the vibration really gives the engine mounts a good workout.

It would be easy to keep it smooth on a V8 as you just run the pistons in sets of 4. 4 working, 4 not working, and with the piston configuration of a V8 it will still stay balanced.

[Dark Horse]

Ah ok, no worries Bossxr8, thanks for clarifying that.

[SSbaby]

Originally Posted by Sox

I poo pooed DOD a while back whilst discussing the so called merits of it with 'ssbaby' on the old forums.

Really? I must have changed my tune since then. :dj:

I wouldn't know if it's any good on freeways as lean cruise does a good job of conserving fuel at constant, light throttle freeway speeds. The biggest saving would be in start/stop city driving (you would think) as that is where most of the energy (from burnt fuel) is lost. If DOD can save 2L/100km in city driving, it would be worthwhile I would think. It's a bit harder to make up that gain on the freeway as lean cruise does a pretty good job anyway.

Besides, manufacturers' claims on fuel economy gains are almost always optimistic.

[irsa76]

All I can say is this. GM did DOD in the late 1970's with Cadillac. As far as I am aware, none still function today, the system that is not the car. Granted it was due to the electronics that the system failed but there is still to much potential for failure.

[One Drone]

Ahh damn, I thought you were referring to a Half Life modication called "DOD" or Day of Defeat.. New version coming out tomorrow lol.

[4Vman]

Yes its an old thread.... but it might be relevant to Holdens announcement.

My theory's on DOD are explained at the beginning.

[Gobes32]

It's simple,

You want cheap motoring, buy a Hyundai Getz

You want a frugal car, Golf Diesel

Something with a bit of passion, An Aussie V8 or turbo 6

YOU CANNOT HAVE ALL THREE ATTRIBUTES!!!!!!!!

[Ohio XB]

Cadillac (GM Division) has a displacement on demand engine


You only need about 50 HP (maybe less) to maintain cruising speed on the highways, so going down to 4 cylinders is no big deal. The whole point is to only eliminate cylinders as demand is decreased, like cruising speed, otherwise you have the full 8 cylinders.

I don't know a whole lot about it, you hear about it once in a while when speaking of technology, but it is not real prevelent in conversation as "Why doesn't everybody do this? It's working amazingly well."

The cost may be a factor, but like I said, I don't know a whole lot about this.


Steve

[BlackLS]

Honda Accord V6 seems to have adopted this technology well.

[ratter]

DOD if done correctly should be able to work and get better fuel economy.

A given car will require X amount of power to travel at a steady given speed, and that will remain a constant based on no matter how many cylinders it has.

But the thing we have to remember is how much pumping losses the motor has, if we awere able to just shut off the fuel to given cylinders to try to save fuel, we would still have the same pumping losses so the other cylinders would have to work harder to remain the same power level.

But if we could also open the valves slightly on the cylinders that are not firing, the pumping losses would be reduced, which would affectively require less effort to run at the same given speed, which should marginally improve fuel economy.


Lean burn does work and was used on LS1's recently on cruise situations which does improve fuel economy as it was running approx 17:1 afr, but the downside is it produces more harmful emissions, which is far worse than saving a little fuel, these cars would not meet current emission levels.
Honda also have or used to have a lean burn engine which ran over 20:1 afr quite successfully, but the fuel was injected at a different angle to a specially shaped piston to get the correct burn, not just a case of lean the motor out.

[prydey]

Originally Posted by BlackLS

Honda Accord V6 seems to have adopted this technology well.

yes honda use this technology and if i remember correctly they tested it in a magazine, maybe even against a falcon, and the fuel economy was .2 or .3 of a L less per 100km. accord was 9.9L/100km v bf2 6sp auto 10.1L/100km. the falcon has .5L more displacement as well.

having read through the thread from the start, i too think its a gimmick. it may work but i can't see it making enough difference to have a major impact. i wonder how much long term testing has been done on it.

regardless of what the media have you think, i believe the engines we have in our fords are very economical for what they are. if we made falcons from the same materials as the euro's then weight would be reduced along with fuel usage. only problem is no one wants to pay $50k for a base model falcon

[xbgs351]

Originally Posted by 4.9 EF Futura

Hey you raise some great points there. i.e. have 8 cylinders making 100kw or 4 cylinders working twice as hard and using just as much fuel to make same power.

That is not true, as an engine is most efficient in terms of power produced per unit of energy, when at or near wide open throttle (WOT). Hence the 'smaller' motor is closer to WOT and will be more efficient.

[xbgs351]

Originally Posted by 4Vman

Yes, lubricating a dead cylinder would require a bit of fuel, aso combustion pressure helps hold the rings in place to reduce oil consumption... too many potential issues for my liking..
Does anyone remember ELB (extra lean burn) in the chryslers? with the lights on the front guards and vaccuum guage on the dash?? it was a failure because it leaned out cylinders and caused detonation and over heat issues..

What do you mean by lubricating cylinder with fuel?

[burnz]

if you look at the current hsv's ls2/3 you will noice the DOD hardwear allready fitted, but not enabled in the softwear.
gm claimed 8% fuel saving and backed by the user.
the valves are closed according to gm for what they call the "spring effect".
all eight pot's are cycled to distribute heat, and being alloy normal heat transference applies.
.
.
wiki
In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation, with the introduction of the Cadillac L62 "V8-6-4" in 1981.

[LPG EF2 GLI]

Originally Posted by xbgs351

That is not true, as an engine is most efficient in terms of power produced per unit of energy, when at or near wide open throttle (WOT). Hence the 'smaller' motor is closer to WOT and will be more efficient.

I'm pretty sure the ECU won't choose to run on 4 cylinders at wide-open throttle. Otherwise the system really is a DUD.

[xbgs351]

Originally Posted by LPG EF2 GLI

I'm pretty sure the ECU won't choose to run on 4 cylinders at wide-open throttle. Otherwise the system really is a DUD.

Your missing the point. The more throttle an engine gets the more efficient it is. Hence a motor running on half its cyclinders will be using more throttle and hence be more efficient.

[madmelon]

Originally Posted by xbgs351

Your missing the point. The more throttle an engine gets the more efficient it is. Hence a motor running on half its cyclinders will be using more throttle and hence be more efficient.

This is exactly right. The DOD would likely use the electronic throttle control to open the throttle slightly as the cylinders are deactivated. This allows those cylinders to achieve a higher "effective compression ratio" and so be more efficient than running all cylinders at a lower throttle opening.

When I say "effective compression ratio", I'm not talking about when the intake valve closes during the cycle, I'm talking about the fact that while an engine might be 10:1 compression, the fact that the air is restricted from entering (throttled) causes a decompression before it is then compressed in the cylinder. A 10:1 compression ratio may only give 2:1 or 3:1 at low throttle openings when viewed in this manner. As compression ratio is a huge factor in overall efficiency (research thermodynamic heat cycles, eg carnot) wider throttle opening means higher efficiency.

[4Vman]

Originally Posted by burnz

if you look at the current hsv's ls2/3 you will noice the DOD hardwear allready fitted, but not enabled in the softwear.
gm claimed 8% fuel saving and backed by the user.
the valves are closed according to gm for what they call the "spring effect".
all eight pot's are cycled to distribute heat, and being alloy normal heat transference applies.
.

In this application holden are reducing power output of the engine by 4%, if the same claims of 8% are made i guess we can see where some of the economy is coming from... looks like a bit of smoke and mirrors.. i wonder what the cost of the option will be?
I wonder how they calculated 8%? was it under all conditions or only while activated? "it ues 8% less fuel while the DOD is activated".. in effect meaning unless you're driving under the right circumstances for DOD to activate it wont help fuel aconomy at all....

[burnz]

claimed in USA 8%...im unawear of holden's claim.
edit: 8% was backed by the motorist whom baught the cars, using cruise control.

[4Vman]

Originally Posted by burnz

claimed in USA 8%...im unawear of holden's claim.
edit: 8% was backed by the motorist whom baught the cars, using cruise control.

They're claiming:


"Depending on driving conditions, AFM will allow Holden’s big V8 to cut back to as few as four-cylinders when driving. In a combined city/highway cycle, AFM can conserve around one litre of fuel per hundred kilometers"

notice the "depending on driving conditions" clause....

If that's right then do the math: the average vehicle travels 15000 k's per year, as long as you mix it up with city/highway travel to use the AFM on average you'll save 150l of fuel, or roughly $170.00 per year... and you get a 4% reduction in power to boot.. boy i hope its a free option!!!

[russellw]

The DoD system as fitted to the Chrysler 5.7 Hemi would seem to be providing fuel savings in the order of 8-10 % based on the experiences of the Australian guys with no apparent reliability issues seen as yet.

There is, however, a noticeable vibration when transitioning between DoD and non DoD modes and a lot of people have noted a drone at 110 km/h on light throttle openings.

Whether the systems have overall merit will depend on your point of view. A 10% fuel saving is probably worth having if it doesn't lead to premature failure of other components but until we see sufficient high mileage cars this is going to be hard to assess.

Cheers
Russ