Would DOD work on a Turbo Diesel?

no-blue-screen · **Posted:** Fri Feb 16, 2007 3:17 pm

Okay, I know some of you are probably going to laugh, but this is a question that I have been asking for quite a while in my head.

A couple of the newer Domestic V-8's like the GM 5.3 LS4, and the DC Hemi 5.7 are using cylinder deactivation (or what used to be called displacement on demand) on their V-8s to gain better fuel economy. Now, my question is for all the engineers and gear heads out there. Would this technology or a similar technology work on a Turbo Diesel? If it were possible, I would think there would be significant milage gains to be had.

Another thought would be an economy/performance setting that would allow for ECU changes on the fly.

My thought is, there are other ways to achieve a significant increase in fuel economy without adding electric motors and batteries to our diesels. I want to be able to have my cake and eat it too....meaning I want great fuel economy, but I want to be able to turn on the power when I need it. The second idea may be one that makes for sense for a Diesel application.

Jeger · **Posted:** Fri Feb 16, 2007 3:47 pm

Im no engineer...But I dont see why it wouldnt work.. The Multiple displacement systems work by keeping the valves closed on the deactivated cylinders and shutting of fuel to them as well, and spark on the gassers. With a variable turbo like we have, overboost shouldnt be a problem, and injectors are electronically controlled as well. Almost seems ideal for a diesel engine doesnt it?

DarbyWalters · **Posted:** Fri Feb 16, 2007 4:08 pm

I would think that on a Low Rpm vehicle like a diesel it would probably be a little more difficult to make it "seamless". Also,by nature, a "turbo" already makes us more fuel efficient by it's nature...off or no boost when no significant load and builds with demand.

BCool · **Posted:** Fri Feb 16, 2007 6:59 pm

a small diesel like ours probably couldn't handle the weight of the vehicle cruising on just two cylinders, maybe three? But if you put a 4L diesel in the jeep and allowed only 3 or 2 cylinders to work you could have really high power and good fuel economy it seems, or just drop in the cummins and have it go from 6 to 2. That could offer a huge amount of power and pretty good economy, but it weights a ton.

huxrules · **Posted:** Fri Feb 16, 2007 7:21 pm

I thought that dod worked by not injecting fuel into the deactivated cylinders. But that the valves still ran normally. Am I wrong- how do you stop valves from operating. If this is the case then it would be easy for a diesel to just not inject fuel.

ATXKJ · **Posted:** Fri Feb 16, 2007 8:02 pm

you stop valves by having a solenoid cut the oil flow to the hydraulic lifter - it collapses and stays closed
(I think there are a couple of fancier ways - but that's the easiest)

CATCRD · **Posted:** Fri Feb 16, 2007 11:34 pm

One of the reasons for the economy benefit of DOD is the reduction of pumping losses by keeping the valves closed. In a diesel engine, there is no throttle plate you're pulling air through, so that benefit is greatly reduced.

litton · **Posted:** Sat Feb 17, 2007 10:22 am

I can't think of any reason it couldn't be made to work if the engine was designed that way from the git-go. The HEMI does collapse the lifters on 4 cyls but there is a fairly complicated sequence that is followed to allow the cylinders to empty (no sense re compressing residual gas on each stroke) then periodically re-engaging the cylinders to ensure even heat distribution. Interestingly, the ignition to the deactivated cyls is not disabled and the plugs continue to fire.

On a turbo diesel engine, the turbo boost volume could be reduced to accommodate fewer cyls, and the injectors could be disabled so it should be feasible......in concept.

It probably can not be make to work on engines with less then 8 cyls though.

To give an example of how well MDS works....at 74 my GC gets ~17 mpg. If I take it to 78 the mileage drop to ~15.5. The MDS does not function at speeds above 75. I can tell by the EVIC when the MDS is operating, otherwise it's not noticable.

spoonplugger1 · **Posted:** Sat Feb 17, 2007 10:41 am

Killing some cylinders on a I-4 wouldn't be the smoothest runner I'd think.
It would take a lot of engineering I'd think to keep it smooth.

RFCRD · **Posted:** Sat Feb 17, 2007 11:07 am

no-blue-screen wrote:

A couple of the newer Domestic V-8's like the GM 5.3 LS4, and the DC Hemi 5.7 are using cylinder deactivation (or what used to be called displacement on demand) on their V-8s to gain better fuel economy. Now, my question is for all the engineers and gear heads out there. Would this technology or a similar technology work on a Turbo Diesel?

This is now old-tech in the big diesel world. Detroit Diesel has this available for some bus applications going back into the mid 90's for extended idling. It's a programming change and can be done due to the electronic unit injection by simply not firing selected cylinders. The problem I saw with buses set-up this way is they idle too cold thus the exhaust fumes are brutal. I have also done this as a diagnostic tool on Detroit Diesel engines with DDECII and later computers. Basically, shut down one cylinder at a time in a rotation to check the balance and response of the remaining cylinders. I did this as a standard check when inspecting a bus engine to find weak cylinders.

DnA Diesel · **Posted:** Sat Feb 17, 2007 8:21 pm

Thermodynaically, a diesel is so efficient, that you would really gain nothing from such a system (that involved the valve train).

Actually, No_blue, if you still have it, your TDI already has it, albeit 0% and 100% DOD. When you're in coast mode in gear, the IQ will decrease to 0 mg/strk until about 1000rpm...that's DITZOD (decreased injection to zero on demand)...

Cheers,
Duey

no-blue-screen · **Posted:** Sun Feb 18, 2007 11:52 am

Don't still have it...but I know what you are talking about. All engine noise disappears when you let off the pedal while coasting. I am just thinking about ways to get better fuel economy other than hybrid electric.

BiodieselJeep.com · **Posted:** Sun Feb 18, 2007 1:22 pm

Not letting my wife drive it improves it 2-3 mpg. My gal like to gun it, bless her pert little butt.

Well, a standard transmission definitely helps mileage. That's a no-brainer and I would really like one on my KJ CRD!

That said, perhaps examining WHY a standard tranny improves mileage could lead you in a dirrection for modification. Shift points, coasting and what-not.

DnA Diesel · **Posted:** Sun Feb 18, 2007 2:07 pm

BiodieselJeep.com wrote:

Not letting my wife drive it improves it 2-3 mpg. My gal like to gun it, bless her pert little butt.

Well, a standard transmission definitely helps mileage. That's a no-brainer and I would really like one on my KJ CRD!

That said, perhaps examining WHY a standard tranny improves mileage could lead you in a dirrection for modification. Shift points, coasting and what-not.

Entirely eliminating any slippage in the TC prior to clucth lock-up, as well as being able to select gears for lower engine RPM at part-throttle.

My 5-speed Jetta TDI and my parents auto TDI (both 2001 models) we great to compare...my Mom is a very conservative driver and she averaged 12-15% worse mileage than my manual.

p.s. NBS, yup, at no-pedal coast, there is ZERO fuel going into a TDI, not sure about the CRD since my VAG-COM/OBDII scanner can't see into the Libby's brains...

Cheers,
Duey

no-blue-screen · **Posted:** Sun Feb 18, 2007 2:14 pm

DnA Diesel wrote:

BiodieselJeep.com wrote:

Not letting my wife drive it improves it 2-3 mpg. My gal like to gun it, bless her pert little butt.

Well, a standard transmission definitely helps mileage. That's a no-brainer and I would really like one on my KJ CRD!

That said, perhaps examining WHY a standard tranny improves mileage could lead you in a dirrection for modification. Shift points, coasting and what-not.

Entirely eliminating any slippage in the TC prior to clucth lock-up, as well as being able to select gears for lower engine RPM at part-throttle.

My 5-speed Jetta TDI and my parents auto TDI (both 2001 models) we great to compare...my Mom is a very conservative driver and she averaged 12-15% worse mileage than my manual.

p.s. NBS, yup, at no-pedal coast, there is ZERO fuel going into a TDI, not sure about the CRD since my VAG-COM/OBDII scanner can't see into the Libby's brains...

Cheers,
Duey

That's a good point....with the TC unlocked....you have power loss....which means lower fuel economy because not all the power is being transferred.

retmil46 · **Posted:** Sun Feb 18, 2007 2:44 pm

no-blue-screen wrote:

That's a good point....with the TC unlocked....you have power loss....which means lower fuel economy because not all the power is being transferred.

That's why I lock out OD when I'm piddling around town in the 35 and 45 mph zones.

As far as something like MDS, I think you'd have better luck dealing with the electronic side of the house. If you could have someone develop an add- on module that does something besides fiddle with fuel and boost pressure, but also tweaks timing and injector duration (perhaps an InMotion tune already does this), that actually has an honest-to-god fuel economy mode, would be the easiest way to bump up fuel economy and shift settings on the fly.

One of the simple mods that the Cummins crowd does to get better fuel economy is an aftermarket crankshaft timing sensor that's adjustable in 1/4 of a degree increments. From reading thru the TDR website and magazine, just tweaking the timing in this fashion, no other mods, gave somewhere between a 5 to 10 percent increase in fuel economy, but one of the drawbacks being it made the engine noisier.

no-blue-screen · **Posted:** Sun Feb 18, 2007 2:54 pm

retmil46 wrote:

no-blue-screen wrote:

That's a good point....with the TC unlocked....you have power loss....which means lower fuel economy because not all the power is being transferred.

That's why I lock out OD when I'm piddling around town in the 35 and 45 mph zones.

As far as something like MDS, I think you'd have better luck dealing with the electronic side of the house. If you could have someone develop an add- on module that does something besides fiddle with fuel and boost pressure, but also tweaks timing and injector duration (perhaps an InMotion tune already does this), that actually has an honest-to-god fuel economy mode, would be the easiest way to bump up fuel economy and shift settings on the fly.

One of the simple mods that the Cummins crowd does to get better fuel economy is an aftermarket crankshaft timing sensor that's adjustable in 1/4 of a degree increments. From reading thru the TDR website and magazine, just tweaking the timing in this fashion, no other mods, gave somewhere between a 5 to 10 percent increase in fuel economy, but one of the drawbacks being it made the engine noisier.

I would rather have more noise and more jingle in my wallet...than a quiet engine that eats more fuel. Heck the noise is the best part about the diesel anyway.

DnA Diesel · **Posted:** Sun Feb 18, 2007 6:51 pm

Ret, the OD-off in town is exactly what I do, as well. What you might lose in slightly higher RPM, I think you gain back in direct connection with the driveline and no slippage. I'd personally like to see shift points lower and TC-lockup happen earlier. The transmission will kill a good engine's usefullness...this is exactly what happened to the Olds 5.7 diesel in late 70's/early-80's....the GM thuds didn't substantively change the programming on the TH350's transmission...they didn't understand that the 105hp, 310ft-lb V8 diesel wanted LOWER, not HIGHER RPM...

Would DOD work on a Turbo Diesel?

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