300C: Not hearing much about cylinder deactivation "feature"

I haven't heard very much (pro or con) about the cylinder deactivation
mechanism that's used in the 5.7L V-8.

Didn't Cadillac try this a while ago and it didn't catch on?

Is there any reliability data on this? Has Chrysler put this in a
5.7L before? (Do / Did the Ram's ever have this?)

(I think this sucks; I wouldn't want it; It will be costly to repair).

 

The Cadilac version if I remember right was back in the early 80's. The
badging on cars equiped said 8-6-4 in a vertical manor. This concept for
shutting down cyclinders when not needed goes back to trucks even earlier.
I wonder if you can just shut this feature off with a dash switch.
_Fred

 

the valves shut off through a lifter bled off and it's a ko0l design
this is one reason it took a a extra year for the car to come out
while it went through r&d testing so i was told .they wanted to make sure
it stayed together
i'm kinda disappointed in the fact the car has no throttle cable and this
system
i'm sure both take away the ability to use horsepower thats hidden in the
engine management system
this system has nothing in common at all with the caddy .system
i go to school this week on it's electronics

 

This I doubt. Extra time to make sure they could incorporate all the
Merc components and hook it up to a Merc transmission - that I
believe.

Ah, so they're not sure the Merc tranny will hold together so they
have a drive-by-wire system to let the computer step in to protect the
tranny.

 

I totally agree. I think the whole concept is one of **much** added
complexity and headaches over the life of the vehicle for **extremely**
marginal gains. Even in periods of low demand when it's running on,
say, 4 cylinders, it can't be nearly as efficient as a full-time
4-cylinder engine because of the extra weight and friction of 4 dead
cylinders. I can't believe the owner will come anywhere close to
recovering the added initial expense by way of (mostly imagined) savings
(even if there are no added repairs due to breakdowns from the added
crap). Basically, a gimmick, of which we have way too many on our cars
already IMO.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Chevy did something like this on the ZR-1 they had a switch that turned off
a
second set of injectors to get a low-power, more economical mode. I
remember
the early reviews on the ZR-1 some of which were under the impression the
"valet" switch turned off cylinders.

I agree with you Bill, I don't think it's worth it. I suspect this is more
sillyness
to get past emissions.

Ted

 

Neither have I.

If by "a while" you mean 24 years then yes... Cadillac tried this
back in '81(ish). It was actually a pretty good system but the
electronics just weren't "there" yet and the tecnical training wasn't
there yet either. Most of them ended up being disconnected and
running on all 8.

As far as I know this is Chryslers first try at this.

Why would you think it sucks when you say you know nothing about it?
It's actually a pretty good idea as you don't loose all that much
energy to the dead cylinders and still have 8 cylinder power and
torque available when you want it. Economical for the work week and a
tire smoker for the weekend. Doesn't get any better than that!

Steve B.

 

OK, Steve. Help me out here.

I'm trying to visualize an eight cylinder engine running on 8 cylinders
and then running on only 4 cylinders with the other 4 free wheeling.
For the life of me, I can't see why there would be less fuel consumed
with a given amount of fuel concentrated over only 4 cylinders than the
exact same total amount of fuel distributed over all 8 cylinders. I
mean, (for that to be true) for a given load (obviously reduced if it's
trimmed back to 4 cylinders), for firing on 4 vs. 8, why would the 4
firing be more efficient than all 8 firing with less fuel in each
cylinder (same amount of power has to reach the driving wheels in either
case, therefore same amount of fuel has to be burned **UNLESS**
efficiency is somewhow magically improved just from the fact of having 4
cylinders firing to produce the same amount of reduced power).

IOW - what it boils down to is: Why is higher concentration of fuel in
fewer cylinders more efficient than lower concentration of fuel across
more cylinders? Honest question - deserves an honest answer.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

I can't imagine the benefit being very great either and have always
wondered about this scheme. Almost every engine is more efficient at
higher throttle settings when the combustion event is more vigorous.
This may be the advantage here. You get 4 larger bangs rather than 8
smaller ones, and the combustion is slightly more efficient when you rae
burning more fuel per combustion cycle. However, I really can't imagine
this being a huge gain. Now if you could disconnect the other 4
cylinders from the crank so that you didn't have their frictional loss,
then I can see it beginning to have some real advantage.


Matt

 

I can see what you're saying about some gains with the 4 cylinders
working harder maybe having some incremental efficiency gain over the
eight working less hard. I still would question the net gain,
everything else (complexity, weight penalty, initial cost, overall
lifetime added cost with just one repair necessitated by the added
immature technology) considered. The cliché "point of diminishing
returns" comes to mind. Would be interesting to see what this vehicle
will get in mpg compared to the old school engine in real world useage.

Here's a nother thing to consider: On that vehicle, the great majority
of fuel usage is not going to be in the low power demand situation when
it can drop down to 4 cylinders. I would think that if it can beat the
regular engine in mpg, it will definitiely not be in stop and go driving
(due to the parasitic drain of the extra weight and friction) - only for
95+% hiway driving - and then it will only be marginal, and the added
costs will never be recovered. Throw in just a little stop-and-go, and
any gains will have quickly been swamped out.

Regarding putting a clutch on a split crank, IIRC, that was done a few
years ago - can't remember by whom (Ford I think, possibly Caddy), and I
don't think it made its way off of the test tracks (even more weight
than just shutting the valve train down). Man - imagine the repair cost
if that clutch goes out (complete engine dismantle).

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

And above all, it can be implemented hydraulically with engine oil
pressure the same way VTEC is done on Honduhs, rather than with electric
solenoids as was done on the Cadillac V-8-6-4(-0) all those years
ago. The latter method has proven very simple and reliable.

 

Because combustion is more efficient the higher the cylinder pressure
is. 4 Cylinders working at 100% of their output are more thermally
efficient than 8 working at 50% of their output, even allowing for the
losses of dragging the 4 unused pistons along (since both valves remain
closed, the only loss is frictional since the energy taken away on the
compression stroke is (mostly) returned on the downstroke).



The efficiency gain was quite measureable back with Caddy's V-8-6-4. The
only problem was horrible reliability, but Caddy attempted to use
electric solenoids to disengage the rocker arm fulcrums on the
deactivated cylinders. There are much better, simpler, and proven ways
to do this, such as the method Honda's VTEC uses to shift cam profiles.
A small electric solenoid diverts oil pressure which then hydraulically
locks or unlocks a pair of rocker arms (one following one cam profile,
the other following a different cam profile. ) In the case of
deactivation the default rocker could just follow a round "lobe" on the
cam or simply rest on a pedestal in the overhead, and the second rocker
would lift it off the pedestal when they're locked together. The
advantage of the hydraulic type system is that the electrical solenoid
is just a controller, the hydraulics do all the work, and the actual
lock/unlock happens ONLY when the rockers naturally align during the
cycle so its a "no load" shift.

 

I think it was the early to mid-eighties. The cadillac v8-6-4.
It died a quiet and timely death.

 

Why do you say that? Even at 70 MPH most cars require less than 1/3 of
their available horsepower. 4 of 8 cylinders should be adequate up to
well above 70 MPH for most vehicles.



Matt

 

Define measurable. 1%, 10%, 50%???

Matt

 

Thanks for the good explanation. I already understood the energy of the
compression stroke being returned in the downstroke, but the bit about
the greater efficiency at higher cylinder pressure took my understanding
to another level - so, again, thanks - that's what I didn't understand.

My only reservation now is the added complexity. If a given component
is divided into, say, 3 new ones with the same total volume and weight,
the cost of the 3 new parts will be somewhere between one and three
times the original one piece. I have to ask how many new parts have
been added to the basic engine to accomplish this, and how much does the
sticker price go up?

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Several miles per gallon. Probably 10%, but I don't remember the numbers
exactly- its been close to 30 years . I do remember tha the V-8-6-4
with a 6-liter (368 CID) v8 got better mileage than the HT4100 (4.1
Liters, about 250 CID) in the same vehicles, AND had a lot more power
available when needed. Come to think of it, the HT4100 didn't hold up a
whole lot better than the 8-6-4 either, which should tell you something
about the state of affairs at Cadillac in the late 70s.... and give
confidence that Chrysler could make a reliable 8-6-4 engine.

 

I was thinking that you could have great mileage for half a tank, and
then do a couple of hours of in-city stop-and-go in which all 8 were
constantly on for rapid acceleration from a dead stop, and the average
for the tank (total miles traveled ÷ gallons used) wouldn't be so good
any more. May not be a fair argument.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

OK, I don't feel like reading all the posts so here is everything I know in
a nutshell. Every magazine test I have read says you can't feel or hear it,
and the time it takes for the other 4 to turn on results in no lag. Also, it
increases fuel economy by 10-20%. When I test drove the car, I couldn't find
any indication of the 4 cylinders shutting off.
Richard

 

It doesn't pay to get into thermodynamics on Usenet. Trust me, there's a
reason. It's more efficient running less displacement at higher pressures to
generate the same power. That's what they're trying to do.