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How'd they do that?

I just read a newspaper review of the current Nissan Altima with the new VC Turbo engine. It is a 2.0 liter turbo 4 cylinder that “…seamlessly changes its compression ratio between 8:1 (for high performance) and 14:1 (for high efficiency) - with an advanced multi-link system continuously raising or lowering the pistons’ reach to transform the compression ratio.” Does this mean the good old fashioned crank rod has been replaced by some kind of high-tech erector set contraption? I tried to do the math but think I missed something along the way; by my computation, a piston on a crank with a 1 1/2" throw (3" stroke) at 5,000 rpm travels at an average of something like 284 mph. I can’t believe that some kind of adjustable rod can last long at that kind of stress. What have I missed?

It’s a weird sorta rocking crankshaft setup. When the engine wants higher compression, a motor rotates the crankshaft mount so that the bottom of the piston travel is raised, effectively making the rod “longer” without actually making it longer, which makes the gap at the top of the piston smaller and therefore raises the compression ratio. Here’s a diagram R&T did to explain it when it came out on Infinitis:

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Thanks a lot. That explains it perfectly, although it looks pretty mickey mouse to me. That said, if it lasts it could be a real game changer.

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Yeah, that’s kinda my big question. Nissan hasn’t exactly been holding itself to typical Japanese car maker standards of quality for awhile, and that seems like a pretty big increase in moving parts that can break.

Guess we’ll see in 10 years if there are a derth of old VC Nissans on the road.

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A multi link adjustable crankshaft and a turbocharger plus a CVT in a car partially owned by a French automaker…What could possibly go wrong?

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A long warranty would help but then who wants their car in the shop all the time.

Yup!
This technology is something that–IMHO–is best avoided until it has passed the test of time in regard to its durability. I’m not a betting man, but if I was, I wouldn’t put any money on Nissan, in light of their so-so reliability/durability record.

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I tried to count the pieces that replaced 1 connecting rod and 1 bearing cap and got lost count after 10. That is absolutely the opposite of good engineering, the main word for which is elegant. The good news is it appears it will an entertaining engine because when it goes, it’s gonna go in a very big way.

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Isn’t it the other way around? 8:1 for efficiency, 14:1 for performance.

Nope. Low CR with high boost=high power. Neat idea, but the tests I’ve read didn’t seem to notice much of a benefit.

I see . It’s b/c of the turbo function. If there were no turbo?

Without a turbo you want high compression for both performance and economy.

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My early 70’s vintage truck’s is in the low 8’s . Apparently the folks at Ford must have been trying to achieve both low performance & poor economy :wink:

Ok. Ok. I know the actual reason for low compressions of the late 60’s, early 70’s was to meet emissions regulations.

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…and with the STELLAR oil maintenance regime that the public at large currently adheres to in this day and age, I am certain that there wont be any kind of problems with this additional and sensitive linkage and other systems used to control this group of additional moving parts.

Yeah I don’t see any opportunity for future issues whatsoever here… Its gonna be great.

P.S. Hey Nissan…guess what other time tested component increases an engines compression and efficiency …on the fly… Ever hear of the Turbo? The entire premise taken by Nismo…is rather foolish imho… neat kinda…but…not in the face of a better method it aint.

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Yes, but you would have to retard the timing under heavy load to prevent engine damage or use very high octane fuel. Ain’t no free lunch.

I just think we are probably in a similar situation like the early 1900’s where there is lots of stuff being tried and eventually something will become the clear winner. I got the new issue of Motor Trend today (might be my last after I canceled it) but there is an article on the development of a new rotary/turbo concept that has some promise. I didn’t read the whole thing yet. Then an interview with Mary Barra who is going full electric with a short stop-over with hybrids because she has to. So it’s a mad dash to get charging stations everywhere to accommodate, whether it will remain the right thing to do or not. While there is a hysterical push to eliminate carbon, there is a blind eye to the environmental and human costs of the batteries required, not to mention the sad state of the grid itself. So we’ll just see what shakes out I guess but at this point like in 1910, I don’t think we should rule anything out to see what actually wins in the market place.

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Can’t valve timing (Atkinson) achieve most of this without the Rube Goldberg stuff?

And there are trade-offs even with electric. That electricity needs to be generated somewhere. The sun doesn’t always shine. The wind doesn’t always blow. Nuclear creates a kind of nasty byproduct. Oil and coal won’t last forever. Probably something like that Honda that came out with a solar panel on the roof will help in sunny climes. Of course, if the power requirements were able to be met (that is to say, enough dilithium crystals could be found), I read somewhere that scientists in Europe were able to successfully “beam” a particle from one platform to another. Hmmmm? Your thoughts, Scotty?

Let me throw Mazda’s new compression-ignition engine into the mixture - yet another neat concept, but years will be needed to show if it is reliable in long term or becomes a nightmare for them

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Sounds interesting. This link (https://www.extremetech.com/extreme/253842-mazdas-2019-efficiency-breakthrough-diesel-engine-runs-gasoline) explains it. Short story: high compression (not indicated) and turbocharged.