Why don't they have engines that can shut off.....

Why don\'t they have engines that can shut off.....

half or more of its cylinders at low load, or during freeway driving?
Is it really that hard to shut off half the cylinders of a V8 while driving on the freeway by just cutting the fuel to each of those cylinders?
What could happen? Vibrations?

Re: Why don\'t they have engines that can shut off.....

Mainly because the valves have to be propped open, otherwise the idling cylinders would cause drag from the compression cycle- It has been done before though, and apparently the benefits weren't great enough for it to be worth the complication.

Re: Why don\'t they have engines that can shut off.....

Cadillac built them back in the 80s... My mother had one and it was always in the shop for engine work. (The rest of the car was pretty nice though).

Re: Why don\'t they have engines that can shut off.

The new Chrysler Hemi's do that. I think they only shut off two cylinders though.

Re: Why don\'t they have engines that can shut off.....

Wasn't there a Corvette with a key to disable half the cilindersfor some reason...? /ubbthreads/images/graemlins/thinking.gif

Re: Why don\'t they have engines that can shut off.....

I believe some of Chrysler's engines have that feature and GM will have that feature available soon if not already. You can do a search on "displacement on demand" as that's what GM is calling their system.

Re: Why don\'t they have engines that can shut off.....

Mercedes had that system in their large V12 engines. They ran on 6 cylinders, and when more power was needed, the other 6 were engaged. The system worked without driver intervention. However, in the very latest version of that engine, the feature was dropped. I guess most people who drive such expensive V12 cars don't really care for the gas conservation possible with this system.

Re: Why don\'t they have engines that can shut off.....

I THINK the Corvette just changed the settings on the computer when the key was turned.
I was said to be for letting your son drive it to prom, or those lead footed guys that park your car for you at a fancy resturant. /ubbthreads/images/graemlins/tongue.gif

Re: Why don\'t they have engines that can shut off.....

I haven't seen or driven any car with this technology but I have my doubts about it. What happens when you really need the extra power (maybe to overtake) and you jam your foot to the floor? How long would it take for the idle cylinders to fire up again?

Re: Why don\'t they have engines that can shut off.....

There is a new car out, I think it is the Dodge Magnum, that does that (8 or 4 cylinders in use). Cadillac did that many years ago with their 4-6-8 engine, offering 3 levele of efficiendy. It requires electronic valve control so the valves stay open on the cold cylinders.

This concept helps, but it does not turn a Cadillac into a Civic. I think it is more of a marketing ploy than a significant gas saver. The single factor that has the most influence on gas mileage is the total mass (weight) of the vehicle, and that does not change when the engine shuts down some cylinders. Other important factors not affected by the engine are aerodynamic drag and rolling resistance.

Re: Why don\'t they have engines that can shut off.....

[ QUOTE ]
maverick said:
I haven't seen or driven any car with this technology but I have my doubts about it. What happens when you really need the extra power (maybe to overtake) and you jam your foot to the floor? How long would it take for the idle cylinders to fire up again?

[/ QUOTE ]

Oh.... about 1/5 of a second.

Re: Why don\'t they have engines that can shut off.....

i think audi did it before to. i realy think it would be cool if they controled the intake and exaust valves with some kinda solnoid. thsat would be cool shut off feul while keeping valvles open

Re: Why don\'t they have engines that can shut off.....

There is ongoing work on ElectroMechanical valve trains. The thought is that infinitely variable valve timing will give the best power/efficency at any RPM.

The Caddy 8-6-2 engine was fraught with trouble!

I want to know why there aren't more Turbo Diesels or even Turbo Gas engines (smaller size).

Re: Why don\'t they have engines that can shut off.....

I think all or most recent volvos have turbo gas engines and all the recent VW diesels are turbo. And VW is the major player in diesel cars right now if I am not mistaken.

So I think turbos are becoming more mainstream than ever before, but there is still a reluctance in many buyers because turbos can be troublesome and expensive to repair. Also, there is the throttle lag problem and they don't help torque very much.

Re: Why don\'t they have engines that can shut off.....

The "Valet Key" on the Vette adjusts the fuel mapping and ignition timing via the engine management system to chop the power output. Neat feature.

Re: Why don\'t they have engines that can shut off.....

The 5.7 L Hemi V8 claims about a 20% gain in fuel mileage at highway cruise. To me 20% is worth it as I spend most of my driving time on the highway at atlest 65mph.

Re: Why don\'t they have engines that can shut off.....

Yep it was done a long time ago. Then it took a while for the turn off ones to come alive. Modern engines with multiport injectors its easier. The next step in engine evolution will be electrically actuated valves instead of cam activated so they can be pushed open to eliminate the compression drag there as well.
Car weight isn't the only factor in gas milage. For example I have a 4x4 truck sitting in my driveway that gets 27mpg and is about the same weight my 22mpg 2wd truck. Manual transmission, drive train, etc all account as well.

Re: Why don\'t they have engines that can shut off.....

New Chrysler Hemi engines have this feature (as stated by others) and the new (rumored) V6 engine for the 2005 Honda Odyssey may have this feature also. Any increase in fuel economy would be a plus if you ask me...

Re: Why don\'t they have engines that can shut off.....

While vehicle mass is indeed number 1, number 2 is engine displacement. emissions controls require a specific fuel air mixture, so unless you are prepared to do as BMW did, which is to actually shut off all fuel to the engine in some circumstances, displacement on the demand is guaranteed to improve fuel economy.

Whether you leave the valves open or not doesn't make much difference, what energy you put in compressing the air, you get back when it expands less some modest losses from leakage. however leaving the exhaust valve open probably makes the engine run a little smoother.

Re: Why don\'t they have engines that can shut off.....

Actually, leaving the valves open will improve efficiency the most. The extra air pumped back into the intake manifold by the disabled cylinders during their disabled compression/exhaust strokes will reduce pumping losses that Otto cycle engines experience at low RPMs.