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")
Joe wrote:
"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
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