I wonder...........if they can control the opening/closing of the valves, can they introduce some valve overlap in the timing, thus letting compression etc out of the cylinder, therefore removing this compression/vacuum effect, in what you rightly describe as a fairly sealed enclosure?
It's just a thought and I like you would love to know the technicalities of it all.
Al.

 

If they kept the valves opening, my thought would be that it would be less power loss overall.

Given the friction losses and that the rotational mass doesn't decrease when MDS drops 2 or 4 cylinders, the final output should be less than half of the original figures. Not that this is a bad thing, but the 4 running cylinders won't be as efficient as a plain 4cyl engine.

Israel

 

With the valves closed, an air spring is created. When you push down on the front end of your truck it comes back up, correct? The same thing happens with air trapped in a cylinder, the work to compress is "recovered" on rebound. Losses are very low for simple springs. True, there is some loss to friction but it is much less than the amount of energy used to basically heat the air in the cylinder, i.e. burn fuel, and blow it out the tailpipe.

I was told from an engineer here (I don't necessarily consider him a reliable source so I don't know if it's true) that cylinder deactivation only happens between 45 mph and 65 mph. Some will say because of the power needed at the speeds outside this window. True, maybe, but I also have talked to another friend/engineer (more reliable, going for Doctorate in engineering) that says the harmonics (no longer a balanced V8, a funky 4) at certain engine speeds create bad vibrations. This seems to be the main reason for when the cylinders cut out.

I remember in high school physics doing a problem that wanted to know how much energy (hp or watts, they are the same) it took for a VW bug to maintain a constant 50 mph. It was only about 15 hp. I remember because it seemed way too low to me. My point is a vehicle, even the behemoth Ram, does not need a lot of energy at constant speed.

I hope this helps.

 

That makes a lot of sense. Given the firing pattern and rotational degree at which each of the remaining cylinders fires, the air-spring concept is probably not as bad as I have envisioned in my head. You will still have losses when compressing the spring, but would regain some of that energy on the rebound stroke.

The balance act with 2 cylinders out versus an even 4 would seem to be more difficult. Reminds me of the HD configuration with the 90deg crank setup and the potato-potato operations.

Israel

 

Springs, including air springs, are more than 90% efficient in returning energy. I don't recall ever doing a spring efficiency problem (BSME degree) but I did read somewhere one of the designers of MDS stated that the loss is "negligible".

 

Thanks for the exchange DCX, I don't often get the chance to talk out theory. Hope I didn't bore you with my low-level thought process!

Israel

 

Yeah, I was going to build my '05 as an '06 and see what the price difference would be, just for fun (okay, I'm hard up for something worthwhile to do). In any event, it would seem I cannot even get past the first page and "build" the truck I ordered last year! Hemi not available in the ST. Just another reason I'm glad I got an '05.

DC's trying to make money anyway they can, but if customers just say, "NO!" Well, we can hope.

All the best.

 

I was able to build mine, it was over 2K more sticker.

So for 2K+ you get...

"a better frame and suspension" OK I agree.
Better looks? Well that is opinion, I like the 05 better, but do like the 06 20s better. God, get rid of the damn gate protector gas saver piece of crap!
3/36 warrnty, no more 7/70 powertrain. Yikes!
Better interior, the changes are minor and I would take either one, neither has anything on the other.
Power badge not placed well on the 06. Petty and minor, but still, I think slapping it on the side of the bed and crooked would look better.
MSD, well holding opinion until some 06 Hemi owners chime in on highway milage.

Over all, I do not see 2k+ of improvements here. The positives and negatives just about wash. Most of the increase I am sure is due to increased fuel costs being pushed to the consumer. We get it from all directions!

 

Does anyone else wonder if this would backfire in the future? I mean its fairly new tech (I guess) and if Chrysler didnt do their homework correctly (which I hope they did) then you could have a V8 under the hood but gettin the power of a 4 banger.

 

Thinking this through... (these are my own thoughts and opinions)

The design deactivates the valves, closing the loop and leaving a sealed cylinder. What happens if the deactivator fails? (is it a fancy lifter with a valve to empty itself and not pump-up and work the valves?) If the MDS kicks back to 8cyl and one of the valve's don't reactivate, what do you get? Intake -- "puddling" of fuel on the back side of the valve that would eventually flow into the cylinder. Exhaust -- a continual circle of firing with no exit for the spent exhaust, which I would imagine would end up forcing itself as blow-by or back into the intake.

As with anything, the more complicated it gets, the more potential points of failure there are. D/C did extensive testing and there are plenty of mid-mileage (50k+ miles) Hemis on the road without such complaints.

The new oil requirements for 5w20 might create a few issues -- its still an exotic blend, so to speak, and I would imagine that the majority of new MDS Hemi owners wouldn't end up with the correct oil up front which might make a difference.

Israel