GM's Displacement on Demand (DoD)

[WhiteXFire]

So I just saw a commercial for the new Chevy Impala SS with the small block V8, and it showed how the car switches between 4-cylinder mode for efficiency and 8-cylinder mode for power. I thought that was a pretty smart idea...make a car that can deliver the power when you want it and still get high gas mileage (28mpg). I see now after reading an article that their first production cars with this feature came out almost a year ago, but this is the first time I've seen it. Here's a nice article on how it works (if you haven't seen it before).

GM's Displacement on Demand
by Jim Kerr

It's finally here. Nearly three years after GM started talking about Displacement on Demand, the first vehicles are hitting the streets with this fuel saving technology. Chrysler actually beat GM to the punch by offering their MDS (Multi-Displacement System) in the Hemi-powered Chrysler 300C and Dodge Magnum RT. Although not interchangeable, both the GM and Chrysler systems utilize components manufactured by Eaton Corporation to cut out four cylinders on the V8 engine and optimize fuel economy.

While Chrysler has started with the passenger car market, GM's first production vehicle with Displacement on Demand (DOD) is the 2005 GMC Envoy XL equipped with the 5.3 litre V8 engine. DOD systems will appear in other GM SUVs and pickups soon. Initial plans are to produce more than 150,000 DOD V8's in the first year and increase production to nearly 1.5 million DOD engines in 2007. GM estimates fuel economy savings of 8% when driven on the standard fuel economy test routine and up to 25% increased economy for some driving conditions. Multiply that by 1.5 million vehicles and the fuel savings are gigantic.

So how does it work and how good is it? DOD uses the power of today's 32-bit engine computer to control valve deactivation, throttle control, injection control and spark advance in an integrated sequence so that the switch between four and eight cylinders is smooth. While GM tried a simplified DOD system on the 1981 Cadillac 4-6-8 engine, the computing power simply wasn't enough at the time. The current engine computer is roughly 25 times faster, has 50 times the computing power and 100 times the memory of the 1981 system.

To switch the engine from 8 cylinder to 4 cylinder operation, the computer operates four solenoids that control oil flow to special hydraulic lifters for the intake and exhaust valves for cylinders number 1, 7 4 and 6. Developed by Eaton Corporation, the lifter is designed so that one section can collapse, or telescope, into the other section. The two sections can be either coupled or uncoupled to each other by means of a locking pin. When coupled, the lifter can transfer the lift of the camshaft to the rest of the valve train. When uncoupled, the lifter acts like a spring and the valve train doesn't move, stopping that cylinder from producing power.

Hydraulic oil pressure, supplied by the engine oil pump and controlled by computer-activated solenoids, is used to dislodge the locking pin and collapse the lifter, thus closing the valve. In reactivation mode, removing hydraulic pressure causes the locking pin to return to its latched position to restore the lifter's normal function. The computer stops valve operation for all four of the cylinders within one engine cycle or two revolutions of the crankshaft.

Synchronizing the throttle opening, fuel injector control and spark advance with the valve deactivation is the difficult part and GM has mastered the programming for this critical sequence. I could not tell when the engine was switching between 8 cylinder and 4 cylinder operation. There are no indicators on the GMC Envoy to indicate it has the DOD system nor any visual indication to the driver that the engine is running or 4 or 8 cylinders. I did notice that the average fuel economy readouts on the trip computer did keep improving as I was cruising or coasting. Sit at a stoplight or accelerate and economy decreased.

During start-up and idle, the Vortec V8 runs on all 8 cylinders for smooth operation. During acceleration, all 8 cylinders provide power but the system switches to 4 cylinder operation during light throttle cruise or deceleration. I hooked up a computer scan tool that GM technicians use for diagnostics and checked out the readings as the system switched. In a short 10 minute city drive route, the system switched between 8 and 4 cylinder operation over 40 times. The only way I could tell this was by looking at the computer data. There was no roughness, hesitations, r.p.m. changes or any other sign of the DOD system operation other than my scan tool readouts.

My experience with the DOD system was very positive. It is totally transparent in operation. There is nothing visible under the hood that has changed - the mechanical changes are internal to the engine. The Vortec V8 engine was smooth and powerful yet fuel economy was very good. I experienced about 25 m.p.g. fuel economy during city driving and over 30 m.p.g. for some highway travel. From studying the scan tool readouts, I found the system is very sensitive to engine load so hills, higher speeds, wind direction and wind speed could all cause a significant difference in fuel economy. Even so, GM's claims of up to 25% improvement in fuel economy seem to be well founded.

[SilverTurboRidin]

pretty cool

[99SL2_Modder]

Old technology. Hemi brought it out in the Mopars a few years ago.

It's been around for quite some time.

And...putting a v8 in a FWD car is dumb.

Nothing now-adays deserves the SS badge besides the Cobalt Supercharged, since it's a new platforms. The others need to be back to RWD before they can be considered SS again. 303 to the front wheels with a v8. Screw that happy horseballs.

*edit*
Well lookie there. It says it right there that GM is slow in development.

[WhiteXFire]

Originally Posted by 99SL2_Modder

Old technology. Hemi brought it out in the Mopars a few years ago.

Originally Posted by OnTheWingsOfCrossfire

I see now after reading an article that their first production cars with this feature came out almost a year ago, but this is the first time I've seen it.

Like I said, I know that it's "old" technology (in development for several yrs, and out for one), but it was new to me. Plus, I figured that with such a large "import" scene, others might not have seen details on how it works.

[koho2731]

Cadillac had the same thing in the late 80's early 90's and nothing but problems.

[MuddyREX]

Gee, why not just make the V8 a little more efficient?? Of make it a hybrid? Hybrid drivetrains are the way the automotive industy is headed, and it seems that GM is running away from it.

[teh DIRT]

Well this is funny. And chris, i hate to say this, your wrong.

I was present last week for a speaker from GM that came to talk about the "environmental substainability". She said a lot of things about cars being the largest polutant in the world. Then she told me something that really shocked me. GMs vice pres was quoted saying that "It is my goal to eventually remove the automobile from the environmental equation". Basically that means that he wants cars to eventuallly emit 0 harmful emmissions.
-pete

[S4toSTI]

Originally Posted by MuddyREX

Gee, why not just make the V8 a little more efficient?? Of make it a hybrid? Hybrid drivetrains are the way the automotive industy is headed, and it seems that GM is running away from it.

i disagree why get a hybrid that does 50mpg when the uk has disiel cars that do 75.

[S4toSTI]

Originally Posted by teh DIRT

Well this is funny. And chris, i hate to say this, your wrong.

I was present last week for a speaker from GM that came to talk about the "environmental substainability". She said a lot of things about cars being the largest polutant in the world. Then she told me something that really shocked me. GMs vice pres was quoted saying that "It is my goal to eventually remove the automobile from the environmental equation". Basically that means that he wants cars to eventuallly emit 0 harmful emmissions.
-pete

And we are surely atleast ten years from that.

[teh DIRT]

oh definitly

[Raven18940]

Originally Posted by teh DIRT

Well this is funny. And chris, i hate to say this, your wrong.

I was present last week for a speaker from GM that came to talk about the "environmental substainability". She said a lot of things about cars being the largest polutant in the world. Then she told me something that really shocked me. GMs vice pres was quoted saying that "It is my goal to eventually remove the automobile from the environmental equation". Basically that means that he wants cars to eventuallly emit 0 harmful emmissions.
-pete

She already owns the company that does that, Saab has been building very efficient, powerful, and clean engines for years. Why don't they just try making a smaller engine with 4 valves per cylinder and maybe a turbo? What about that new 250 hp 2.8 V6 turbo?

oh and, 300hp V8 + FWD + soft amercian suspension = crazy torque steer.

Chevy: engineered like a rock.

[S4toSTI]

I am sorry but when we are talking about real fuel effiency here we are no longer talking anything that is a v6 or v8. We are talking about 1.3 gasoline engines or 1.3 turbo diesel engines. Anything more then that drinks gas period. Over in the uk france italy they get this and gas is so high there that a prius is not worth it. You my friend of all people whould know this, ebing an avid top gear watcher like myself, that they are not messing arround anymore. Honda jazz's and ford ka's these are cars with tiny engines that get mind blowing gas mileage. Anyway back to the point i think this is a step in the right direction for the americas however very far from where we need to be. One day gasoline is gonna run out and it is gonna be a bad day. Methane power cars and alcohol powered cars need to begin to catch on along with electric... this hybrid bs is just delaying the inevitable.

[Raven18940]

And despite the high price of petrol, cars that actually move are still popular. Turbo 4's are the future, my huge sedan gets 35 mpg at a 55 mph cruise, way more than that impala SS could ever hope to get, and I can still almost keep up with a STI at WOT. My car doesn't even have variable valve trickery either, just a really well designed cylinder head and a clever ecu. Chevy/GM has the technology and know how right under their nose, but they're too stuck in their good ol boy, pushrod past to realize the future.

[S4toSTI]

I agree and disagee, i think they are gonna try to milk this gas guzzaling cow for as long as they can. Heck if ford is making or made an escape that is a hybrid i think we are getting somewhere. Side note is that sti you speak of stock?

[1988 Olds]

It's a cool idea but look at the LS2 in the new corvette. Thats rated at like 21/28 and has another 100hp. I think they could make another 2-3mpg if they lowered the HP.

We are alot farthen then 10 years from no emissions vehicles. Even if they stop making cars that use gas there will be millions and millions of people who still have gas powered cars.

[LSHatch]

The human race will die before we truly harm the planet. And after we are gone, it will regenerate and adapt to what we left behind. This is the truth. It's adapted many times already.

[S4toSTI]

Originally Posted by LSHatch

The human race will die before we truly harm the planet. And after we are gone, it will regenerate and adapt to what we left behind. This is the truth. It's adapted many times already.

Can i see you proof on this.

[OutOfStock]

Eh Earths gonna be ****ed eventually, we'll all be dead by then but the Moon is slowly moving away from the Earth. Its gonna **** some **** up when it goes away, like earths rotation on its axis and all that mumbo jumbo lol.

[LSHatch]

Originally Posted by S4toSTI

Can i see you proof on this.

Human race. Disease. War. It doesn't matter what it is. Earth has been here much longer than we have. Who says a meteor doesn't crash again? Or another ice age? Stuff like that has happened.

We WILL die before the Earth does.

[blkbomber01]

they tried that about 20 years ago... i think they were in olds and they were called a v8-6-4.... same idea but back in the day they were junk, in and out of the shop.... hope they did better with this one