Displacement on Demand

[jikelly]

Howdy Ya'll,

I wasn't sure if this would count as strictly classic tech so I posted it in talk.

Anyway, I was watching the speed channel the other day during one of the rare airings of a non nascar automotive show and I saw a guy talking about GM's new Displacment on Demand system being used on its latest version of their V8 engines. Basically it turns off engine cylinders to allow the large V8 engine to reduce its displacement and fuel consumption.

Does anyone know if Ford has developed a similar system for their engines? What I'm really waiting on is a hybrid V8 I can modify and shoehorn into my 73 but until then variable displacment might get me to consider moving to a mod motor when my current engine dies. Hopefully that won't be for a long, long time.

 

[Max Power]

Never heard of Ford doing it, nut GM and Dodge have done it. The new Hemi from Dodge shuts down cylinders through hydraulics in the lifters.

When looking at hybrids, you have to do a cost benefit analysis. Right now, the present new hybrids give up their mileage gains in purchase price and battery replacement. The benfit to an individual is purely feeling good.

 

[10secgoal]

Yep ford has. It drops the pulses to the injectors to make it a dead cylinder I'm told. I was try ing to get one as a u-hual for my trip cross country. I didn't get one. I got 6.8 mpg.

 

[10secgoal]

Never heard of Ford doing it, nut GM and Dodge have done it. The new Hemi from Dodge shuts down cylinders through hydraulics in the lifters.

When looking at hybrids, you have to do a cost benefit analysis. Right now, the present new hybrids give up their mileage gains in purchase price and battery replacement. The benfit to an individual is purely feeling good.

But don't forget about the tax break you get. I will be buying ford's new escape. I will feel good, but " It's about principalities, SMOKIE ! " Messin' with gas prices is like messin' with my emotions.

Did anyone else get that but me ? Probably not.

 

[DarkBuddha]

Yep, I've read about "displacement on demand" for the last few years, but it hasn't been isolated to new car manufactureres. With the development of stand-alone engine management systems (like TEC II), I've heard of folks like Trepanier doing the same sort of thing on some of his projects with tradition pushrod motors. It seems simple enough in theory... program an algorithm for the engine management computer that takes certain input data (like vacuum readings, O2 sensor readings, maybe throttle position, etc.) and then doesn't fire the injectors or plugs for whichever cylinders. I just wonder how you decide which cylinders to drop... maybe it has to do with balancing the stress on the rotating assmebly?

My point is that with some good research and some well spent dollars, I'm guessing you could probably achieve something comparable to "displacement on demand" without spending wads of cash on a late model conversion.

Hope this helps.

 

[67GTA-FB429]

Couldn't you do it by putting a rev limit on the motor at 2500rpms? That would make cylinders drop out at random...

 

[rbohm]

ford in fact along with eaton was a pioneer in the displacement on demand system. they started working on a system in the late 70's that would shut off cylinders to reduce both emissions and fuel consumption. while ford has continued developement over the years, they have not made a system for public consumption due to cost, reliability, and other concerns.

 

[ForceFed70]

Most of these systems do help a little with mileage, but not alot.

There is so much more to fuel efficiency than just displacement. Reciprocating mass for example will stay the same.

It's a step in the right direction, but it will never give you the fuel economy of a 4cyln while running on only 4 cylinders.

It's been used/tried in 1 sort or another for many years. In fact, your EGR system is a primative version of displacement on demand. Exhaust gasses enter the cylinder effectively "taking up space" and lowering your would-be displacement.

 

[10secgoal]

Yeah, i can't imagine it would work to well. It still has to drag around the weight of the piston.

 

[jikelly]

I remember reading about GM's system a long time ago when they first started looking at it seriously. Apparently what 70 Nitro said is true. It was like they had to find a way to shut the valves of to the cylinders they wanted to eliminate in order to prevent pumping losses. I guess that is so the engine is not working to compress the air that would stream into the unfueled cylinder, or maybe the air traped in those cylinders becomes like a spring?

Anyway, it is a really good idea, and I hope the manufactures continue to develop it. Because gas is not getting any cheaper.

 

[rbohm]

I guess that is so the engine is not working to compress the air that would stream into the unfueled cylinder, or maybe the air traped in those cylinders becomes like a spring?

the air trapped int he cylinder acts as a spring thus you get a zero sum loss(the work generated equals the load created), as the friction losses remain the same.