It seems that everybody has the idea that there is a technological silver bullet that will give SUVs the fuel efficiency of passenger cars. In reality, an SUV is inherently fuel ineffienct, and it doesn't matter whether you're talking about old-fashioned body-on-frame ground pounders or car-based softroaders.

First, despite any improvement in coefficient of drag, an SUV will always have a relatively large frontal area. Secondly, they're inherently heavy. The Chrysler Pacific crossover tips the scales at over 4500 pounds, and all of the Rendevous and Muranos are two-tonners as well. You can play with hybrid drivetrains, but you still have leff efficient vehicles.

Lastly, Displacement on Demand incurs engineering liabilities that are far greater than succesful technologies such as multivalve heads and VVT. You still have unballanced inertial forces, unless you seek very complex and expensive remedies - something I can't even conceive of from my limited engineering knowledge.

GM orchestrated a very public failure in this area, and in my opinion, should have abandonned the idea altogether, and permanently. The 4-6-8 was utterly worthless, unlike the Oldsmobile diesel which ran well enough but required engine rebuilds within 50,000 miles.

If anything, a return to domestic diesel engines for passenger cars and light trucks would be a better idea than DOD. With the switch to low sulfur diesel from 2006, it would actually be a desirable course of action.

 

I know I am late with this comment but I have to say that I like the sound of a LS1 better. Me and my old man had a 396cid stroker Ls1 in our old 99 vette with log tube headers and a very lound exst. It sounded like a badd *** big block at idle and part throttle and like 100 crotch rockets with subwoooooofers at 7200 rpm. IMO i havnt heard a better sounding pass.

 

Silver Bullet? No, but just because SUV's are inherently inefficient doesn't mean they can't be less inefficient. In fact, improving the economy of the least efficent vehicles has the most profound effect on the amount of oil we consume.

I don't know how you can continue to site failures that occured over twenty freakin' years ago. Pac-Man wasn't even out yet. The Russians were still our enemy. Bill Gates was working on a "Disk Operating System" (DOS) for IBM. The V8-6-4 wasn't even computer controlled. Technology has come a long way. There's a saying "If you always do what you've always done, you always get what you always got." I think GM remembers the failures and the risk. I also think they know the risk of not doing anything at all.

BTW, diesel engines for passenger cars are a great idea. Jetta TDI's get 50MPG. Just think how efficient they could be with DOD.

 

Could you explain what you mean by unballanced inertial forces? Not trying to flame, just want a better understanding of this potential downside to D.O.D.

I can see how crankshaft torsional loading will change in 4cyl mode, but even then, it isn't neccesarily unbalanced, and really isn't that critical during low-load operqating conditions.

 

I think he's talking about the nature of a 60-degree or 90-degree engine and how there's an inherent imbalance caused by the piston trajectories versus gravity and versus each other, etc. By contrast, a "boxer" engine or an "H-4" like some of Subaru's engines is theoretically perfectly balanced internally.

Am I even close to the mark? gt

 

You've got the right idea. Hypothetically, the only perfectly balanced engines are flat fours and sixes, straight sixes and 60 degree V12s. There's alot more to it though. You also have primary and secondary order forces, some of which can be corrected with balance shafts, and others which can't be solved entirely.

DOD means that your 60-degree V6 will be running on four cylinders part of the time. I'm not entirely clear on how smooth a de facto V4 would be. In any case, these engines should have a better technical basis than the old V8-6-4.

Another unanswered question is whether an OHV engine with "Displacement on Demand" will have variable valve timing and lift. Siemens developed a suitable VVT system for pushrod engines back in the early 90s. However, no manufacturere picked it up. Since DOD shares alot of conceptual similarities with the Siemens concept, there is a tantalizing possibility of trully hight reving OHV V6s and V8s. Any takers for a 7000rpm LS-6?

 

The LS6 already revs to 6500. Redzed, I'd personally want to see an LS6 to 8000 rpms just to scare import enthusiasts with such a high revving V8

 

Mmmm.. a 7000 rpm LS6 with VVT

it be able to keep the low end tq, mild manners, and emissions down below...

and have the more radical valve timing for high rpms flow

A tq curve thats even more flatter and wider

and even better fuel efficiency

all at an affordable price?

That would be a dream.

 

Regarding a V4's smoothness, I've owned several Honda V4 motorcycles, and can honestly say they are the smoothest motorcycle engines I've ever experienced. The V4 configuration has perfect primary balance, and a very negligable secondary imbalance. Both 180 degree and 360 degree engines exhibit this balance. In contrast, a inline 4 has relatively large secondary imbalance, and there is also a primary imbalance due to the separation of the crank throws. The BMW boxer 2 cyl engine has the same problem. In X-Y plane, it has perfect primary balance, but in the X-Z plane, it has a large imbalance due to the large separation of the crank throws.

I doubt a GM DOD engine in 4cyl mode will have any significant vibration. From what I've gathered, one problem will be greater intake noise, due to only 4 cylinders operating at a larger throttle opening. Expect more silencing desinged into the induction system.