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The Pub For General Automotive Related Talk |
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#31 | ||
HUGH JARSE
![]() Join Date: May 2005
Location: Yap-Hoon
Posts: 21,567
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OK so my post was a little bit tongue in cheek.
After all you can't have everything |
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#32 | |||
beep beep
Join Date: Dec 2004
Location: Melbourne
Posts: 1,971
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Quote:
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.
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Nothing to see here, move along, move along... Last edited by parawolf; 23-09-2005 at 11:57 AM. |
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#33 | |||||||
RIP...
Join Date: Dec 2004
Posts: 15,524
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Even so, I remain very sceptical on the longevity of such a design. Quote:
The reduction in torque will require greater throttle openings to achieve the same result. Catch 22. Quote:
If it was a good thing, BMW would have been using 10 years ago. Rick.
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. Oval Everywhere... |
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#34 | |||
FF.Com.Au Hardcore
Join Date: Jan 2005
Posts: 14,654
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Quote:
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...!
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335 S/C GT: The new KING of Australian made performance cars.. ![]() |
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#35 | ||||
Irregular Member
Join Date: Sep 2005
Location: Glen Waverley, Vic
Posts: 356
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She mostly takes
![]() *** Wheels magazine COTY 2004 *** I usually get: Mitsubishi Magna ES (TL 2004) *** Wheels magazine COTY 1996 *** |
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#36 | ||||
RIP...
Join Date: Dec 2004
Posts: 15,524
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Quote:
The must be some kind of valve deactivation for there to be no upstroke compression losses. Quote:
Rick.
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. Oval Everywhere... |
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#37 | |||
FF.Com.Au Hardcore
Join Date: Jan 2005
Posts: 14,654
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335 S/C GT: The new KING of Australian made performance cars.. ![]() |
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#38 | ||
_Oo===oO_
Join Date: Dec 2004
Location: Canberra
Posts: 1,471
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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.
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#39 | |||
Irregular Member
Join Date: Sep 2005
Location: Glen Waverley, Vic
Posts: 356
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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: Quote:
Mind you, I'd probably wait a while before buying one myself! |
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#40 | |||
Peter Car
Join Date: Dec 2004
Location: geelong
Posts: 23,145
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#41 | ||
_Oo===oO_
Join Date: Dec 2004
Location: Canberra
Posts: 1,471
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Ah ok, no worries Bossxr8, thanks for clarifying that.
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#42 | |||
Banned
Join Date: Dec 2004
Posts: 689
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Quote:
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.
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#43 | ||
Snoopping
Join Date: Jan 2005
Location: In front of the 'puter
Posts: 626
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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.
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#44 | ||
Lane HO
Join Date: Dec 2004
Location: Sunshine Coast
Posts: 386
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Ahh damn, I thought you were referring to a Half Life modication called "DOD" or Day of Defeat.. New version coming out tomorrow lol.
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#45 | ||
FF.Com.Au Hardcore
Join Date: Jan 2005
Posts: 14,654
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Yes its an old thread.... but it might be relevant to Holdens announcement.
My theory's on DOD are explained at the beginning.
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335 S/C GT: The new KING of Australian made performance cars.. ![]() |
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#46 | ||
FF.Com.Au Hardcore
Join Date: Mar 2006
Posts: 2,021
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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!!!!!!!! |
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#47 | ||
Compulsive Hobbiest
Join Date: May 2006
Location: Ohio, USA
Posts: 1,032
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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
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#48 | ||
yum
Join Date: Jan 2005
Posts: 1,417
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Honda Accord V6 seems to have adopted this technology well.
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#49 | ||
FF.Com.Au Hardcore
Join Date: Feb 2005
Location: Pit Lane
Posts: 11,867
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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.
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#50 | |||
Rob
Join Date: Sep 2006
Location: Woodcroft S.A.
Posts: 21,551
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Quote:
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 |
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#51 | |||
FF.Com.Au Hardcore
Join Date: Mar 2005
Location: Vic/NSW
Posts: 2,687
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Quote:
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. |
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#52 | |||
FF.Com.Au Hardcore
Join Date: Mar 2005
Location: Vic/NSW
Posts: 2,687
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#53 | ||
VFII SS UTE
Join Date: Apr 2007
Location: Central Coast
Posts: 6,353
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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.
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I don't often hear the sound of a screaming LSX. But when I do, So do the neighbours.. GO SOUTHS
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#54 | |||
Starter Motor
Join Date: Nov 2005
Posts: 18
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Quote:
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. |
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#55 | |||
FF.Com.Au Hardcore
Join Date: Mar 2005
Location: Vic/NSW
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#56 | |||
FF.Com.Au Hardcore
Join Date: Nov 2006
Location: Sydney
Posts: 1,334
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Quote:
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. |
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#57 | |||
FF.Com.Au Hardcore
Join Date: Jan 2005
Posts: 14,654
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Quote:
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....
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#58 | ||
VFII SS UTE
Join Date: Apr 2007
Location: Central Coast
Posts: 6,353
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claimed in USA 8%...im unawear of holden's claim.
edit: 8% was backed by the motorist whom baught the cars, using cruise control.
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I don't often hear the sound of a screaming LSX. But when I do, So do the neighbours.. GO SOUTHS
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#59 | |||
FF.Com.Au Hardcore
Join Date: Jan 2005
Posts: 14,654
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Quote:
"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!!!
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#60 | ||
Chairman & Administrator
![]() ![]() Join Date: Dec 2004
Location: 1975
Posts: 107,049
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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
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