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

You're getting to the meat of it now; in 1981, Cadillac had ONLY the V864
and the Olds Diesel to pick from. Tough year. In 1982, they had only the
HT4100 and Diesel. Even worse year. At least the V864's could easily be
converted to regular 368's. There wasn't anything you could do with the
blockless wonder HT4100.

Mechanically, great strides have been made that have allowed, among other
things, variable valve timing to seem perfectly ordinary and reliable. Valve
defeating is easier than that.

 

Running at higher pressures is independent of displacement though. The
comment was that smaller displacement cylinders yielded lower emissions.
I've seen not data that supports that. Higher compression ratios
might well accomplish this, but that is not a function of cylinder
displacement. Running at higher temps also increases efficiency, but
again that isn't a function of displacement either.


Matt

 

Thanks - that was made clear by others after I posted.

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

 

"Blockless wonder" indeed. Very apt.

To be honest, the biggest problem the HT4100 had was that it was an
engine of a size and cylinder geometry that made it suitable for a car
the size of a Camaro and it was put in a car the size of the Queen Mary,
and so they all spent their (short) lives running flat-out and lugged
down. Its "evolved forms"- the 4.5 and 4.9- were actually pretty decent
powerplants. Not in the same league as the Northstar, but not terrible.

 

Matt,

While the phrase "running at higher cylinder pressure" could mean a
couple of things, rather than taking it to mean higher compression
ratio, in the context of the discussion (since the demand for power will
represent a greater percentage of the smaller engine's total
capability), for a given power demand in the same relatively heavy
vehicle, I took it to mean that the throttle on a smaller displacement
engine will have to be open much wider, so there will be less intake
vacuum, and more air will get packed into the cylinder - in effect, with
a smaller displacement engine with the same nominal CR, the actual
cylinder pressure will be higher due to being much closer to WOT
operation (than you would be with higher displacement).

Then again, since the term is ambiguous, maybe I'm reading it all wrong
but it made sense to me with the interpretation I gave it.

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

 

That could be, but it would be much more clear to say running at a
higher power output. And again, this isn't an inherent efficiency gain
due to smaller engine size, it is just better sizing the engine to the
car from an efficiency perspective.

Yes, hard to say as several of the concepts proposed seem pretty murky
to me.


Matt

 

As long as, by "higher power output", you mean as a percentage of the
max. capability of the the two engines (one high displacement and the
other low displacement) being compared as opposed to absolute power
being demanded at the moment (which is equal for the two engines for the
efficiency comparison). Again - from context it was clear that's what
you meant. (Might as well get rid of that ambiguity too though.) 8^)

But describing it as due to higher pressure (cylinder packing) or less
intake (throttle plate) restriction peels one more layer off the onion
in understanding (than simply saying "it's more efficient because it's
more efficient". In that sense, it was indeed an inherent efficiency
gain, which to me is the same as saying the engine size was matched
better to the application for efficiency as you put it - I see the two
wordings as being in agreement. In fact in my case, when it was claimed
that a smaller engine was inherently "more efficient" in the same power
demand situation seemed like some devious hand-waving, but when it was
explained in those other terms, the proverbial light went on.

This brings up a question: For the given power demand, if the smaller
engine is having to run at 99% of its maximum (I'm givin' her all she's
got. Captain!! She can't take no more!!"), is that the most efficient
operation? My gut says no - that there is some max. efficiency point
that is somewhere greater than 20% and less than 90% of max. So in that
sense, smaller would not necessarily mean higher efficiency for the
given power demand within the engine's capability.

True - I did not understand all of the explanations - I wasn't sure if
it was due to my shortcomings or those of the explanation.

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

 

Yes, I nearly said high specific power output, but then figured everyone
would wonder what that meant!

I believe that the maximum efficiency point for a given engine is the
point at which it is producing maximum torque at WOT. The horsepower
typically peaks well above the torque peak, so the maximum efficiency is
almost always less than the maximum HP output from the engine.

I don't think the shortcomings were yours. The statements may well be
correct, but it certainly isn't obvious that they are and they seem to
me to not follow logic. I'd like to see some data or a bona fide
reference that supports the claims.


Matt