Whatcha think about Hemi cylinder deactivation?

Discussion of the 5.7L-6.1L-6.4L HEMIs.

Moderator: scottm

Post Reply
User avatar
scottm
Posts: 3121
Joined: Wed Aug 29, 2001 7:00 pm
Location: Texas
Contact:

Whatcha think about Hemi cylinder deactivation?

Post by scottm » Mon Jan 05, 2004 6:04 pm

http://www.thehemi.com/news.php?id=20040105-4

What does everyone think about cylinder deactivation being
used on the 5.7 Hemi in the 300C and Magnum RT in 2005?

Can anyone explain the details? It says it keeps the valves
closed in four cylinders. Does the air not compress in those
cylinders? Or does the compression not ruin the efficiency?

DCX says the motor was originally designed with this in mind.
So hopefully that means the system is going to work correctly.
They have 7 years or 70,000 miles worth of faith in them. :)
Scott Moseman
http://www.TheHEMI.com/
Follow us: Image & Image

HappyKillMore

Post by HappyKillMore » Tue Jan 06, 2004 8:40 am

I think it's an interesting concept, and it should be fun to see how well they end up working. I won't be buying one, of course-- if I wanted the efficiency of a 4-cylinder, then I'd buy a true 4-cylinder. I must admit though that with as many steady highway miles I rack up, I wouldn't mind seeing a little more efficiency! :wink:

As for the actual technology, if the lifters turn off at or near the end of the exhaust cycle for a given cylinder, then there wouldn't be much in the cylinder to compress. If that's the case, then there shouldn't be much of an inefficiency created there.

giddie
Posts: 25
Joined: Thu Oct 09, 2003 5:59 pm
Location: San Antonio,Texas
Contact:

Cylinder Deactivation

Post by giddie » Wed Jan 07, 2004 6:36 pm

I think this is a great idea and would be elated if it were as simple as a PCM flash to add this feature to an 03 Hemi (I can dream). Hopefully modern technology will make this work better than GM's attempt in the early eighties.

It seems to me that even if the cylinder is empty, everything expelled on the exhaust stoke before the valve closes, then the cylinder would then be fighting vacuum on the down stroke? During the down stroke of ignition the cylinder is filled with expanding gasses but if there is no flame (an expanding gas) then won't a vacuum be created because the air between the piston top and combustion chamber is being forced to expand? Would this create vacuum? If it does, would it make any significant difference?
Jason O'Brien
2003 Black Quad-Cab 1500 Hemi*
http://www.giddie.com

HappyKillMore

Post by HappyKillMore » Thu Jan 08, 2004 8:19 am

Yeah, there would be some vacuum fighting if you exhausted then turned off the valves. I would think that overcoming that vacuum would use less energy than fighting compression. That would depend entirely on how strong a vacuum you created, and that vacuum would be strongest at the bottom of the stroke. Given the shape of the combustion chamber, there would still be a volume of exhaust gas in the chamber at the end of the exhaust stroke; how much would depend on the pressure differential in the manifold. In the end, I don't know how hard a vacuum you'd create. You could mitigate it though if the exhaust valve closed early, thereby leaving some gas in the cylinder. You'd be fighting some compression and some vacuum, and that may be the happiest medium.

I wonder about closing off the valves though. Since the entire valve train is driven by a camshaft, I don't know how you'd "turn off" some of the valves. I suppose you could have two different cam shafts, one of which could be clutched in and out as needed. That would seem to me to be overly complicated. I would speculate that it would be much easier to just turn off the fuel at the injectors and to turn off the spark plugs. All you're really trying to do is not use as much fuel, so turning it off is the simplest solution. If this is how the engine actually works, then DC could theoretically write a program for our current trucks.

Anyone else care to speculate? Or to tell me I'm full of it? I don't suppose anyone who works for DC would be able to shed light on this for us...

User avatar
scottm
Posts: 3121
Joined: Wed Aug 29, 2001 7:00 pm
Location: Texas
Contact:

Post by scottm » Sat Jan 10, 2004 5:41 pm

On the DaimlerChrysler media website, they have a
Real Video demostration of the valvetrain and how it
works with the MDS. Both valves on the stopped cyls
are in the closed position. I find that very interesting.

I am not quite sure how to describe how MDS works.
There is this contraption between the cam lobes and
the pushrods. When a cylinder is "deactivated", the
contraption will "give" as the cam lobe presses on it
and it does not pass the movement to the pushrods.

Sorry if my description is weird... hard to explain. :)
Scott Moseman
http://www.TheHEMI.com/
Follow us: Image & Image

charger r/t
Posts: 1
Joined: Tue Nov 25, 2003 8:54 pm
Location: San Antonio Texas

Post by charger r/t » Sat Jan 10, 2004 9:20 pm

I only hope this technology will be unobtrusive to the average non-automotive enthusiast. Many still remember the horrible Cadillac V-8-6-4 of 1981. I honestly have my doubts about this. Would it make any sense to explore a way to defeat the system, possibly through the aftermarket?
2002 Dodge Neon SXT
2003 Chrysler Town & Country LXi
1976 Chrysler Cordoba 400 V-8

HappyKillMore

Post by HappyKillMore » Sun Jan 11, 2004 11:33 am

No Scott, that makes sense. I think that the more complicated the system becomes, the more ways there are for it to break.

As for allowing this system to operate or defeating it, maybe this MDS will just be an option. I don't think it would be a noticeable problem anyway, since it allegedly takes place in just 0.040 seconds!

94bird
Posts: 16
Joined: Thu Dec 05, 2002 2:34 pm

Post by 94bird » Sat Jan 17, 2004 11:13 pm

I haven't had a chance to drive a 300C with MDS in it yet, but my friends who have say it's unnoticeable. Sooner or later I'll get my hands on one.

Post Reply