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Extreme Economy Tune

2K views 27 replies 16 participants last post by  Powerstrokinva 
#1 ·
I am just trying to promote an educated discussion here. This may have been thought of already.

I was wondering about some of the trucks now a days that shut down 2 or 4 cylinders based on load and throttle position and was wondering why something like that hasn't been done (that I am aware of) on the 6.0? It seems to me that it is something that could be done with a tune, maybe interrupt the electrical signal to the injectors.

Say your cruising down the highway or in town and you could flip a 3 position toggle to turn your 6.0L V8 into a 3.0L 4Cyl, or even a 4.5L 6Cyl. I could see it vibrating more due to the "misfire" but what if you could have it rotating through the cylinders, for instance just say it is hitting on all 8 cylinders, and if you flip to switch to "6 cylinder mode" it would interrupt the fuel to cylinders 1 and 2 for that rotation, then cylinders 3 and 4, then 5 and 6 and so on. I am sure there is a way based on firing order to interrupt the fuel in a way, that you would still have 1 cylinder firing on each stroke, instead of having 1 stroke where there is no firing. that would help to minimize the "misfire" vibration.

At least that way if for example you left it on 6Cyl mode for long periods of time, the "wear" on the engine could stay fairly even, versus shutting fuel on cylinders 1 and 3 the entire time, by having the misfire "rotate" through the firing order.

What made me think of this was the fact that one of my soldiers had a nice gmc sierra that would basically rotate between being a 4, 6, or 8 cylinder engine based on load, and the fact that on the highway without towing and cruise control set, he was breaking into the 30's for economy.

Whaddya guys think? Maybe some one more educated can "learn" me as to whether this would be good idea or not.
 
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#2 ·
It isn't done via a tune or strategy change in the new ones. It also hasn't ever been done on a diesel. I think there is actually some sort of control module that controls fueling and all other parameters for that. When I sold cars for a living for Chrysler they had just came out with their version of the MDS Multiple Displacement System. It had flaws at first but they were able to work it out and it eventually seemed pretty neat. I don't think it will ever be a possibility for the 6.0 for something like this.
 
#3 ·
Interesting idea...
 
#4 ·
Aproaching 30 mpg, yea right. Those trucks would be sold out. Not calling you a liar, i'm calling him an embellisher of the truth. Shuddering, is what my truck did when it dropped an injector.

Sent from my phone that somebody didn't help me get.
 
#5 ·
^^ I agree. Even with the MDS working properly on the hemi's they still were lucky to break 18mpg. They went to the MDS cause of fuel economy yes but for example the Hemi was getting 10 - 11 MPG with out the MDS and around 15-18 depending on driving habits, weather, location, type of driving etc. No where near 30 MPG. If 30 MPG was possible with these systems than everyone would be driving a truck with these systems. My wife's 07 focus gets 30 in town and 40 on the highway. Saying that a half ton v-8 truck could do the same is ludacris.
 
#6 ·
he told me getting close to 30. It wasn't my truck, so it is being told here 3rd hand.

I am thinking about some of the commercial trucks when they turn the jake brake on, it also cuts fuel to the appropriate cylinders (some of the older ones would still deliver the fuel) but if something like that could be done here. I use my truck as a daily driver and the average speed for my commutes between home, to post, and then driving around on post is probably around 30 mph average. I drive easy on the truck because frankly there is no room, and no need to get on it on post. anyways it sounds like a possibility. I would think it would be similar to to just simply unplug 2 injectors, but that would not have the same ease of driving, I think it would simply miss to much and to hard making it a pain in the *** to daily drive, but if it could rotate through all 8 cylinders in a sequence based on firing order, and a few other things i.e. throttle position, load etc. I think it would be fairly strait forward to drive.

It is cool to think about, according to the lie-o-meter i get somewheres around 20-22mpg on the highway (cruise set on about 61-62mph) and that is 6 liters of displacement. so in theory if you could run at those speeds on a "3.0 PSD 4CYL" you certainly wouldn't double your mileage because there would be more load on those 4 cylinders, but maybe you get upwards of 28-30MPG' s according to the lie-o-meter. LOL

Does anyone see an issue with interrupting the electrical signal to the injector? I mean would it pose any sort of mechanical issue I may be over looking?
Any suggestions on possible issues with this set up, or one similar to it?
If I knew anything about writing tunes, I wouldn't be afraid to write one and then "test drive" it around the block a time or two and start improving it from there.
 
#7 ·
Just to give you an idea there are over 4000 different parameters that can be altered when writing a custom tune. Getting someone to sift through all 4000 and arrange the possible correct match of parameters is a needle in a haystack type situation.
 
#9 ·
The issue with shutting off the injector is, fuel also acts as a cushion to prevent injector tip contact with piston.
 
#10 ·
On gas engines, the engineers have to focus on keeping the proper air fuel ratio around 13-14:1 i believe. The multi-displacement engines turn off fuel and spark on those cylinders it's shutting off.

On diesels, there isn't a focus about air fuel because it could be 2:1-100:1. Take a look at the injector pulse width while you are driving. Sometimes it turns off the injectors completely on all cylinders...

Something to think about also is the harmonics of the engine when just a couple cylinders are turned off . There is a lot more involved than just turning off a couple injectors...
 
#11 · (Edited)
I understand about the air fuel ratio, because engine speed in a gasser is controlled by manipulation the amount of air entering, and fuel. In a diesel the engine speed is controlled by fuel alone, so that should make it a bit easier to do something along these lines. Also by "shutting off the fuel" I mean interrupting the electrical signal. there will still be pressurized fuel at that particular injector, but when it's time for that injector to get the signal to spray, it would simply be skipped for that rotation of the crankshaft. then the next time around that injector would get it's chance to fire, but another one in the cycle be skipped for that rotation of the crankshaft and so on and so on.

I understand what your saying about the harmonics of the engine, but that is why I think it would have to be 2 or 4 injectors at a time that are getting skipped, but it couldn't be the same 2 or 4 getting skipped every time.

I have ridden in a few of the multi displacement engines, and really when it would go from 8 cylinder to 6 or 4 cylinder i really didn't notice much of a misfire type vibration(although it's been awhile since I rode in one). In theory it seems as though it would work based on the fact that there are 4 strokes in each cycle. we have 8 cylinders, so we would have 2 pistons creating power on each of the 4 strokes. If you skipped 4 injectors, in the correct order, you would still have 1 piston creating power on each of the 4 strokes, minimizing vibration.

I don't know though, I mean i am assuming if you unplug even one connector on any random injector and then tried to start you truck up as a 7 cylinder I am pretty sure it would be a noticeable mis fire, you would know right away something wasn't right.

There has to be something I am overlooking, based on the fact that a 4 cylinder engine runs fairly smooth, and so does a 6 cylinder engine, but if you unplug one injector on the 6 cylinder it would noticeable, even though the 4 cylinder would be running smoother with less cylinders.

It's gotta be something along the lines of each power stroke created by each individual piston compliments the other pistons in there rotation, rather than just mathematically on paper:
8 cylinders /4 strokes= 2 power strokes per cycle= one smooth rotation of the crankshaft.

Well none the less, this is good stuff, really making me think here. With our powers combined we can either figure this out, or de bunk it. :D
 
#12 ·
interesting idea. I dont know nearly enough about the 6.0, or diesels for that matter. :rofl:
 
#13 ·
You need to get rid of the drag/compression for it to work. Variable valve timing comes to mind or an extra decompression port.
 
#14 ·
+1 Very nice point.

Maybe something like a jake brake type setup that could keep the exhaust valve open to say 10 thousandths, just enough to leak compression into the exhaust, but not enough for the piston to give it a high five. Well you would also have to stop the intake valve from opening, otherwise you would leak boost into the exhaust system.

At least now we know it's not as simple as a tune. would have to be some sort of tune and jake brake combo.
 
#15 ·
what if you didnt shut off any injectors but reduced the pw on 2,3, or 4 so you didnt have a dead miss. There may be a way to inject enough fuel to cover the feel of the miss but still save on fuel overall. I feel the savings would be minimal though because your not making the power needed to keep the truck moving without giving more throttle.
 
#16 ·
I believe an 8 cylinder running on 4 cylinders would be inherently smooth running. Then again 4 cylinder engines typically aren't in a V formation.

You are going to lose a lot power on the compression stroke of the dead cylinder. It's possible any fuel savings is going to be used up by this alone. The 4 cylinders are going to use more fuel to keep 4 extra cylinders moving around.

One more point, if an diesel engine engineer hasn't already done this there is probably a reason.
 
#17 ·
the other thing is as soon as one cylinder is weak, never mind dead, there is less hot air to spin the turbo. so now boost drops off, the cylinders that are "supposed" to be working have less boost, make less power. Rpm starts to drop the computer has to try to compensate by increasing power to the cylinders that are firing....the whole friction/compression loss. it would actually be more doable if the engine was fully supercharged instead of turbocharged. end of the day it would be expensive and probably the actual gains would be minimal. especially since the general idea of these trucks is that they are expected to be loaded heavily enough that they need 8 cylinders all the time.
 
#18 ·
Another thing to keep in mind is that diesels operate very efficiently with proper tuning. That alone will net you more mpg gains than tryin to come up with a MDS type system for one. Take a F250 gasser and a F250 powerstroke stock for stock and see which one gets better mileage. The diesel will win every time as it doesn't have to work as hard to produce the hp and torque needed to propel such a heavy vehicle forward. This is why they say "more power less fuel" as they can increase the power without using a lot more fuel and allows the engine to perform more efficiently while producing more torque and hp to keep the heavy mass moving forward.
 
#19 ·
And one thing about the 4cyls, they are inline, ever notice how an inline engine seems to be smoother the a v type configuration? THat's why the cummins can run as smooth as silk and even a well tuned stroke or dmax will still have some rattle. Pushing straight down vs diagonally makes a huge difference.

The mds would be neat on these as there are more and more of them used as DD's vs towing all the time. As it sits now, what other 7500+ pound vehicle is capable of 15mpg or more? I can't think of any.
 
#23 ·
Diesels run most efficiently at cruise, while gas motors do at WOT because they are throttled and waste energy producing vacum, on a gas motor , multi displacement works because the remaining cylinders operat with less vacum, a diesel will have less combustion efficiency in the remaining cylinders because the ratio of fuel to air will need to be richer to produce the same power rerquired to push the truck down the road.
 
#24 ·
so in order to make something like this a reality, you would need some sort of variable valve timing, or jake brake type setup, to avoid fighting the compression on the "dead" cylinders, as well as the tune to manipulate the injectors, and jake brake/ variable valve timing accordingly.

I would say that while it is still feasible at this point, it is also de bunked at the same time. At least for a small time mechanic like myself. Thanks for the suggestions and hurdles.
 
#26 ·
Cadillac had that technology on there cars in the 90's. I'm sure there is a good reason it is not being utilized in diesels. This will be a good topic for someone's thesis.
 
#27 ·
This is still an interesting concept to think about. Some of the best ideas come from asking completely unrelated questions.
 
#28 · (Edited)
Some additional info on displacement on demand systems from my experience:
The GM DoD (Displacement on Demand) system deactivates up to 4 of the 8 cylinders by both cutting the fuel and locking the valves shut to prevent dry pumping of the cylinders. It will fire the spark plug off every two compression strokes to keep the cylinders that are deactivated warmed up. There are several (dozens) of other factors and algorithims used to prevent engine damage/excessive wear and tear/and driver perception issues. The DoD system uses pressurized oil to lock out (technically unlock i guess) the lifters and prevent camshaft lobe movement from transferring through to the pushrods. Pressurized oil is directed to orifices of the lifters by electronically controlled solenoids. The engineers actually designed a nice, neat little package that drops into the valley of the V8 and is almost completely self contained.

Now I am not an engineer but that is a rough version of what I remember from my GM training programs when I used to work at a Cadillac dealer.

The reason you don't feel vibration in those systems is for one they only activate at part load/part throttle conditions where you wouldnt notice two or four cylinders not firing and because they drop specific cylinders based on the firing order so that the affected cylinder's companion cylinder (cylinder in the same position of crankshaft degrees but on opposite stroke) can make up the difference in crankshaft rotational speed.

I think it is entirely possible to adapt a similar system onto a turbo diesel but I doubt the associated development and implementation costs would out weigh the small fuel mileage gains. Not to mention that a large portion of 3/4 ton and up truck buyers are not particularly concerned about fuel mileage.

You never know though there might be ford engineers in a small, dimly lit, skunk works type office working on this right now!
 
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