Totally different thought here gents. Think pure weight rather than motor efficiency. OEM's value lbs per vehicle as much as any efficiency numbers. Day to day work I see high value per weight reduction numbers that say lighter power trains will win the day. Typical numbers that drive decisions are $10-20/lb reduction with far higher numbers for weight/target challenged vehicles ... Cough cough Fiat/Chrysler...
Given this I see smaller lighter powertrains leading the way....
You can see that in the new Miata engine - it's really light. Really impressive. But it comes at a cost - the walls of the head are so thin that you can't port it, and there's no room in the block for an overbore.
In reply to Keith Tanner:
I would think that the weight difference is minimal (what isn't metal will be water) but it should come to operating temperature a whole heck of a lot faster.
IIRC slow warmup is the reason Nissan never sold the RB in the US. There was so much metal in the engine that they didn't feel they could get the engine to operating temperature quickly enough.
We don't put water in the crankcase, generally 
The engine is also fairly small, and looks shrinkwrapped around the greasy bits. It really is light.
Knurled wrote: I would think that the weight difference is minimal (what isn't metal will be water) but it should come to operating temperature a whole heck of a lot faster.
The density of water is 1 g/cc, whereas for aluminum it's 2.7 g/cc, so even if it all turned into water jacket it'd still be a lot lighter.
codrus wrote:Knurled wrote: I would think that the weight difference is minimal (what isn't metal will be water) but it should come to operating temperature a whole heck of a lot faster.The density of water is 1 g/cc, whereas for aluminum it's 2.7 g/cc, so even if it all turned into water jacket it'd still be a lot lighter. If the block capacity is say one gallon, then the weight delta from water to aluminium is only 13lb's or 6 kg if you like (rounded to whole #'s for clarity) Not massive in the grand scheme.
I think the point being made is that with the new Miata engine it's such a small, compact, efficient design that the actual quantity of water in the block is so small that even going up 2.7 times on density, the over all weight woudn't change that much as there just insn't that much water in there.
I have no dog in this fight, I just like engines with character. I love my turbo 5 in the Volvo. 90% of peak torque by 1,800rpm. No, it's not a modern small capacity engine, but it's great fun to drive. I can rocket off of corners using all that torque and have great fun. I also love my severely torque (and power) challenged Boxster, it's actually a very slow car by modern standards, but it's fun to wind it out to the rev limiter and oh my (insert mythical deity of choice) it sounds glorious at full chat. I like both.
I wonder what the future will bring. So in the short term everyone is already on small capacity turbos, in the medium term we're now talking larger capacity NA engines. But I think we all know that internal combustion engines and cars as we know them are, if not on life support, closer to the end of their current epoch (can machines have epochs?) Ultimately we're heading head long towards autonomous electric or hybrid cars. In the meantime what are we likely to have? High performance hybrids are becoming more and more commonplace. I think within 15 years most self-driven cars will be some form of hybrid. When you can run an IC engine at peak efficiency as an electricity production device what is the more efficient, I'll bow to Eric (Alfadriver) here, but I'd guess small capacity forced induction?
In reply to Adrian_Thompson:
I disagree that we are that near the epoch of ICEs.
If we were, everyone would be copying each other exactly, as it would the the last, optimum design.
In consideration of the Sky motor, I've added a third option to my list of where to go:
1) optimize and improve the existing powertrain and do a better match with the trans and vehicle system. This is Mazda's path- where they made the engine lighter, higher compression, found more efficiencies in design, etc.
2) make the engine much smaller, and boost it to have the appropriate power- which is the path many are taking right now. But seeing what we are doing right now- we are not nearly at the peak of what this can do. Nobody has the best powertrain system, yet. And some OEM's have individual parts that others just don't do well. To me, this path has quite a way until we really narrow it down to an optimum set up. Bear in mind- we do learn a lot from each other. There are some really interesting new tech that is also coming which shows a lot of potential (but I can't really mention what it is).
3) make the engine bigger, and put hardware on it to have it run smaller. AKA variable displacement. At the moment, this is largely NumCyl and NumCyl/2 in terms of running options, but there are developments that will allow any number of cylinders to run at one time. If anything, this is the tech that will allow larger N/A engines. What we don't really know is if it can actually be done without making the customer really angry, and at a cost that makes sense.
With the huge advantage that ICE's have in terms of fueling (many parts), it's going to take a while for EV's to really displace them especially given there's still room.
In terms of EV's- one thing that is mentioned is charge speed increases. That helps hybrids make a lot more sense, too- as energy recovery can be at a much higher rate. And there are some interesting things for micro-hybrid ideas- more like the Honda Insight vs. the full blown Hybrids today.
As much as some like to deny it, there's a whole lot going on, and a lot of potential still on the table.
In addition, if the NOx problems can be solved, lean burn (like Honda experimented with in the 90s) can get some significant gains as well with less complexity than cylinder deactivation.
Implementing a lean cruise in the tune on the Jeep (cruises at about 15.7:1 AFR in closed loop instead of 14.7:1 with increased timing for the slower burn) was worth about a 5% MPG gain around town (mixed driving) and around 10% in highway cruising. The gains are more significant at lighter engine loads where it makes a bigger difference in pumping losses (due to having the throttle further open for the same power output). Comparing the current setup (with a mild cam, improved heads, lean cruise tune, etc.) to stock, I can cruise at 75 on the highway and get the same or slightly better MPG than it did cruising at 60 stock (and at a given speed on a given long highway drive, it's about 15% better than stock).
A more modern engine would be able to go even leaner for larger gains. I haven't really pushed the limits on my setup, but I doubt I can get it past 16:1 and still have a good burn. Higher compression and faster burning chambers would help a lot there.
In reply to alfadriver:
Eric, I don't doubt your knowledge or opinion on ICE's. I'm sure there is a long long way to go, but I think it's outside factors that will force the change. Not necessarily the current or future science and technology within the field.
ICE's and more specifically cars are an easy target within the pollution arena. Forget the fact that cars are actually very efficient and have made massive strides that would have bet against 15 years ago. Forget that in the overall scheme of things automobiles are a relatively small part of the issue. Forget the fact that with all electric cars the electricity has to be generated somehow and that is still a) a massively polluting industry in its own right, b) has looming infrastructure issues and c) alternative fuels like ethanol are currently an environmental nightmare due to our subsidies or corn. Forget that we could save a hell of a lot of resources and pollution by keeping and maintaining the cars already in existence rather than building new ones (while putting both of us out of work!!!) Forget the all the actual facts. The facts is most people see thousands of cars a day, so they are a big, easy to target, they are a very noticeable as a source of perceived pollution. Also, forget the enthusiasts. The coming generations, many of the current generations and especially older generations are waiting to dive headlong into autonomous all electric cars. We hear time and again that people used to a brand new iPhone or exploding android every year don't understand why we don't have autonomous electric cars already. I see the rate of advancement in electric cars, governmental pressure (which itself comes from the populace), will push standalone ICE cars into an early grave. I do believe that we will have ICE/Electric hybrids for a long time to come though. So, that being said, true or false in reality, what do you think will be the way forward for a small ICE to run at constant speed as part of a hybrid drivetrain.
Note This is not an anti-climate change post, I believe in that completely, I'm just pointing out that ICE's are an easy target to legislate against for the feel good factor. – Please no flounder. Just stating my personal beliefs, not doubting anyone else’s, we’re all entitled to think what we will.
In reply to Adrian_Thompson:
Agreed. Although the ICE is far from it's developmental apogee, the cost and complexity of improving them only increases from here. While the cost of EVs goes down. For many of the reasons you stated I think it's entirely possible that ICE are never fully developed because it won't make financial sense, or there will no longer be enough demand to justify the effort.
In reply to Adrian_Thompson:
They can be an easy target for those who don't want to see them. The real issue these days are totally ineffective rules- EU- I'm looking very much at you.
Good rules work well, as they do here in the states.
But there's an overwhelming number of people who want personal transportation that does not cost a massive fortune. And there's probably close to 1B cars on the road around the world. It's going to take a very long time to find a solution for 50% of those.
In reply to rslifkin:
If anyone can solve the lean NOx problems, diesels become an option again.
alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.
Good point!
rslifkin wrote:alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.Good point!
I've posted this before- there are some really good problems to solve that can make someone a LOT, LOT, LOT of money.
I heartily encourage anyone to think about it.
alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.
Drop compression, lose the turbo, and go back to 40hp cars and 110hp trucks?
Eric, any comment or insight into the news around Germany wanting to ban internal combustion engine cars by 2030?
alfadriver wrote:rslifkin wrote:I've posted this before- there are some really good problems to solve that can make someone a LOT, LOT, LOT of money. I heartily encourage anyone to think about it.alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.Good point!
Didn't VW already come up with the solution? giggity 
alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.
There is a solution, it's called selective catalyst reduction. Otherwise known as that really expensive extra tank you have put a different funny smelling fluid in.
Also, see natural gas engines. Diesel torque levels, gasoline emissions (or better)
Adrian_Thompson wrote: Eric, any comment or insight into the news around Germany wanting to ban internal combustion engine cars by 2030?
I don't want to put words in his mouth, but we had a discussion about it last week:
https://grassrootsmotorsports.com/forum/grm/germany-looking-to-ban-ices-by-2030/122637/page1/
In reply to STM317:
Had not seen that somehow. Off to read now. Cheers
maschinenbau wrote:alfadriver wrote: In reply to rslifkin: If anyone can solve the lean NOx problems, diesels become an option again.There is a solution, it's called selective catalyst reduction. Otherwise known as that really expensive extra tank you have put a different funny smelling fluid in. Also, see natural gas engines. Diesel torque levels, gasoline emissions (or better)
I know about that- it's very expensive, isn't as effective as it needs to be, and does not work for lean gas cars.
While it works, it's the reason I don't think you will see smaller diesels in Europe as we enter 2020.
In reply to Adrian_Thompson:
BTW, I stopped posting in that thread a while ago. Made my point, moved on.
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