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Discussion Starter #1
:thumbsup I know we have a lot of smart experienced diesel folks on this forum. Maybe you can help out with a crazy idea we all can benefit from.

I want to be able to shut off 3 cylinders whenever I wish.:rof

I know 3.35 liters and 175 hp is plenty for everyday city and freeway driving with no load. I don't know how much fuel it will save to shut off 3 cylinders but I expect it will be 2-4 mpg.

An inline 6 is well balanced and can run on 3 cylinders (chosen for correct firing order) and still be well balanced so vibration shouldn't be a problem. Since these are diesels it seems all we have to do is unplug 3 injectors. I figure the computer will throw a fit and not allow the engine to run if you just unplug the injectors. So, as usual, we have to come up with a way to fool the computer.

I have driven lots of diesels in Europe, Asia and Australia and they all had tiny little power plants and get fantastic mileage. Of course they are a bit slow but so what they work. If we can make this work we could get the best of both worlds. Tire shredding power when we feel like it and economy if we choose.

Please be nice if there is something obviously stupid about this idea. I'm not a diesel engineer.
 

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The only thing stupid about this idea is that you do not realize that oil interests would not allow this to happen in North America.
 

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The technology is already working in gas motors. Part of the problem as I see it might be that a gas motor can also shut off the spark to the dead cylinders. A diesel by virtue of not having spark plugs might be at a disadvantage in that area. However altering the valve timing on three cylinders might do the trick. But it could be difficult to achieve given the clearances between piston and valve might not be sufficient?
 

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I'm not sure cylinder deactivation actually works with diesels. Gas motors have better efficiency with larger throttle openings and cutting off cylinders is a way to force that. Same thing with the Corvette's incredibly tall 6th gear. Since a traditional diesel has no throttle I wouldn't expect greater efficiency. I dont' know how the ETC plays out in my theory.
 

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You shut off three cylinders, and you will need to inject more fuel into the remaining three to get the same power. The only way you gain anything is if your engine burns fuel more efficiently when more fuel is injected; it probably does a little bit. You might pick up 1-2 MPG if you're cruising at relaxed speed and weight. Or you might loose 1 MPG if our engines are more efficient at burning low amounts of fuel. Or, most likely, you wouldn't notice a thing except for it sounding funny.

You're just not putting fuel into those cylinders; you still have the weight and friction of the cylinders and valve train to overcome.

Provided that you wanted to do so, the common rails are the only trucks that'd be capable of doing it. Just don't open up the injector every other time... Does EFI Live let Duramax people do that?
 

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Discussion Starter #7
Begle 1 - You are correct but I don't want the same power. I want half the power to save fuel.
 

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Discussion Starter #8
OK I did some internet research. Bad news. Variable displacement engines are not that great. Best case you can expect 5-8% mpg improvement. Well at best that's 1-2 mpg's. Not worth the trouble. The problem is the parasitic and pumping losses of the dead half of the engine. The only way to get 30+ mpg like the foreign trucks is to use a small engine. Bummer.
 

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You could add an overdrive unit to the rear shaft and bring the cruising rpm down to 1200-1300 like a big rig runs.
 

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I had the variable engine in my jeep grand cherokee. The 5.7L Hemi and I got horrible mileage all the time. 11 around town and 17 on the hwy. It would come on between 40 and 55 MPH I believe so it was never on while going faster then 56 MPH. I saw on one post where the 6.7L Cummins is only using 27HP at 65 MPH so there should be a way to get some fuel savings. One great idea is to get rid of the DPF system :butt:
 

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I like the idea - if a Gas chevy motor can do it, I dont see why we couldnt have it happen. Even if it just ran on 4 cyl, alternating the 2 that are getting fuel, only while crusing it could help. The gassers that do this do not run in 4 cyl mode when accelerating - just cruising when there is not much strain on the engine. I wonder if one of the companies that makes our chips could come up with something for us
 

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I have a hemi work truck with the displacement thing and after 20K miles it still doesnt get near as good fuel milage as the cummins with only 17K miles

Even if you did cut off 3 injectors U still have to deal with the compression produced by the dead cyls or its just another load on the engine and would hurt fuel milage.

driving habits and a few good mods are still the best
I Think
 

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My wifes 07 tahoe has the cylinder deactivation. What a joke. It has a display that tells you wether it is running on 4 or 8 cylinders. at 70 on the highway (mind you we are in illinois, so flat ground, no hills) I would say it is in 4 cylinder mode approximately 10 percent of the time. if 4 cylinder mode saves 20 percent fuel, and its only in that mode 10 percent of the time, Im saving 2 percent on that deal as opposed to not having it. What a joke
 

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I think the smarty cuts off three holes with their high idle feature right? I don't see why it wouldn't work. I did that on an old big cam III cummins I had. I just used it while idleing though. It seemed to help. The problem with doing that on a gas engine is the torque curve doesn't really start coming up until 2500 to 3000 rpms. Most cruise at about 1800 or so. So when you cut off half the motor there is not near enough power to get it down the road. In a diesel the torque comes in much lower. I think this is a plausible idea, just don't know if it would really work. I think it's worth a shot anyway, but like you said, I'm not a diesel engineer either.
 
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