Engineering thoughts: Vehicle efficiency.

[MinisterofDOOM]

So I'm fairly well-known for my dislike of four-cylinder engines and my "couldn't care less" attitude toward fuel economy. Pretty much everyone else, though, seems to feel otherwise. Now that gas prices are rising again, I feel like everywhere I turn someone is asking me about fuel economy (being "the local car guy") or complaining about the price of a fill-up, or bitching about 1 or 2 pointless MPGs.

Amidst my annoyance, I've started to wonder if the solution isn't right there in front of all of us, disguised as a compromise. My question is a simple one: WHY are we reducing cylinder count ALONG WITH displacement? Yeah, yeah, I'm a V8 elitist and couldn't find a place in my garage for a compact car if gas was $30 per gallon. But honestly: why aren't we building 2 liter V6es and 3 liter V8s?

It seems so obvious. Look at trucks and big V8 sedans. Cylinder deactivation, VVEL/Valvetronic, direct-injection and all sorts of fancy tech stuffs dramatically improves fuel economy without impairing performance. It's the best of both worlds. So why on earth are we not scaling this DOWN? Think about it: an Accord with a 2 liter V6. Run it as a V3 or an I3 (whichever's smoother or provides the best operational balances) or even a V- or straight-twin when power needs are minimal. Or a G35 with a 3 liter V8. Scale back to 6, 4, or even 3 cylinders based on power-consumption. Combined with individual-valve-control tech like VVEL or Valvetronic, you end up with a powerplant that offers HUGE versatility, from economical cruising to around-town efficiency all the way up to tire-shredding and drool-inducing exhaust notes. Add forced induction on-demand in concert with those technologies, and you could go from a miserly, gutless 2-cylinder to a scorching 350+hp V8 all in the same package.

You could even implement some static and dynamic programs to control the desired results. On the drive to work, you can hit the "Economy" button and limit engine operation to 4 cylinders and 200hp or less with conservative shift settings and a low redline. But after work, feeling the need to work off some stress, you hit "Performance" mode and get all 8. 3 liters of V8 madness scream to 7000+ rpm and all your worries disappear. No reason to over-restrict operation, though. Intelligent programs could vary cylinder use, fuel mixtures, and other variables to get the best economy or best power available on-demand, or all the time. Plus, when Junior gets his driver's license, you can lock him in 150hp mode and tie it to his keyfob. No hoonage in the high school parking lot for him.

It seems so obvious. Yes, I understand two banks of cylinders or even additional cylinders means more parts, more complexity, and more cost. But we're throwing tech, parts, and complexity at engines left and right these days anyway (just look at a diagram of a VVEL valvetrain!). More cylinders means more options and more versatility. And aluminum blocks and the compact design of V-format engines means there's very little difference in weight, especially if we're designing to be small in the first place. Imagine a 2 liter V6 that fits in the space of a 4-cylinder (and before you complain about width, take a look at the intake and exhaust manifolds hanging off each side of your 4-cylinder engines. Look under the hood of an S2000 and tell me a straight-4 is small). Imagine an ultra-compact V8 that's as small as, or smaller than, modern "big" V6s.

It seems silly to me that we scale cylinder count with displacement. Twenty years ago cars had 3 liter V6s and 5 liter V8s. Now everything has 3.5 liter V6s and 6 liter V8s. But our 3.something-liter V6s are making more power than those 5 liter V8s did 20 years ago, and we're STILL increasing displacement. If we've come that far...from 160hp out of 3 liters (53 hp/liter) to 330 out of 3.6 (91hp/liter) why the Hell haven't we started scaling SIZE back, so we're looking at 200hp out of 2.2 liters? Or 250hp out of 2.5 liters? Or...etc, etc.

Yeah, pumping losses will be present while in reduced-cylinder-count-mode, but efficiency overall has come so far over the past decade that I will argue that's not an issue, especially not when you can minimize by closing valves, etc.

I want an Altima with a 2 liter V6. And not a VQ; I want a V6 designed to displace 2 liters from the ground up. No bigger than 2.5 at max. Scalable down to 1.5 if needed.

I love my tiny 3.9 liter V8. I want to see more like it.

EDIT:
Also HORRAY FOR CHROME and it's tab restoral function. Just as I finished this post, the power went out ("emergency repairs" affecting 2000 people in my area, apparently). I swore loudly, and the idea of typing all of this again was making my temples pulse. But I rebooted the PC, started up Chrome and "would you like to restart the tabs from your last session?" Yes I would!!! And praise Leto, all the text from my post was intact, too.

[Kompresshun]

YES on all counts. I seriously think we need to copy these posts to the homepage at some point. These would be excellent homepages features every so often.

I don't really understand the infatuation with going to smaller, 4cyl forced induction engines. They are producing slightly better results in most cases, so why not apply the same ideas to V6 and V8 engines? My I30 gets 21mpg in the city and 30mpg on the hwy, so why in the heck would I buy a 4cyl Ford Fusion that gets 23/31 instead?

Of course I don't get the whole obsession with fuel economy anyways. Gas prices start rising and people freak out, go out and trade their Camry in for a Prius. Not caring about extending their loan terms, or raising their car payment, because all they care about is the figure they see when they fill up the tank.

I wrote an article on it a while back and it is simply amazing how much extra you would actually spend by trading your vehicle in for something more economical. The math almost never works out to be even close to an advantage, no matter how you look at it.

[alms24sebring]

Thats a great point and Ive wondered this myself when the turning off of 4 cyls in a v8 for economy just started coming around. Why not make it for a V6? Maybe running in 3 cyls is too hard for the motor since it has another 3 dead ones, but still it can run on an even 4 cyls. I would also rather see smaller motors since V8 hp numbers from the 90s can be achieved with a 4 or 6 cyl today easily as you said. I think the pros outweigh the cons by far. Who knows maybe there is alot more logistics involved than we think or a great increase in manufacturing techniques. But everything will be made in China anyways so whats the problem with cost? Money will still be made

At the Washington Auto Show, there were ALOT of new ideas on display and everything had a small turbo for economy, with a hell of alot of electronics that is. This guy representing Ford was telling me that (some ford concept) would pull air and fuel in on the intake stroke but then squirt alittle more halfway up the compression stroke to decrease temps by 10-15%, thus slightly bumping hp numbers. With some detailed and intracate timing, the motor could be very efficient and still produce the power. Id much rather have a small super economic turbo'd 2.0 liter V6 than a 90hp 1.5 liter engine with a weaksauce hybrid setup. If a hybrid's not getting 60+ mpg, I dont want it.

And hail to Chrome, that's happened to me twice. I absolutely HATE retyping stuff over especially when you are done with it.

[PapaSmurf2k3]

technically, cylinder de-activation isn't as efficient as the other methods for increasing fuel economy. You still more or less suck in the same amount of air, and therefore burn more or less the same amount of fuel. You might save a tiny bit of "work" done by the engine by leaving the valves open, but at the end of the day, Engineers are working more on increasing an engine's efficiency of turning a fuel into energy that propels you forward. Current internal combustion engines are getting better, but still really don't crack 30% efficiency.

A 6 stroke diesel with a water injection (second power stroke) would be MASSIVE gains in efficiency. You'd be turning all that wasted heat energy that we currently circulate through a heat exchanger known as a radiator into power. Exhaust gas temperatures would be much lower too.

Realistically, ALL belt driven accessories can be driven off turbines in the exhaust system.

Direct injection is good, but the internal combustion engine still needs an evolutionary leap in the form of gaining another ~30% efficiency. Nuclear power for that matter does as well. Bleeding off enriched radioactive materials to boil water and spin a turbine at 20% system efficiency is kinda dumb if you ask me.

[redtop91]

My question is a simple one: WHY are we reducing cylinder count ALONG WITH displacement? Yeah, yeah, I'm a V8 elitist and couldn't find a place in my garage for a compact car if gas was $30 per gallon. But honestly: why aren't we building 2 liter V6es and 3 liter V8s?

I agree. The thermodynamics of Otto cycle by which IC engines work doesn't factor in stroke cycle for output work purposes (at least in simplified analysis) but I'm positive I'm nowhere near the top of my class as far as engineering goes and the engineers involved with engine design are probably at the upper echelon of understanding. I'm venturing that heat rejection becomes a major concern when you decrease displacement and maintain cylinder count. The only way to do that would be to make the stroke remarkably short which would make pumping exhaust at a significant rate difficult and the cylinder head would have to be pretty responsive not to interfere. I'm probably just babbling but those are some notable obstacles that I feel like would pop up. I'd like to hope they've considered this and there is a sound reasoning behind not doing it.

If I'm totally off base here then this is what I will do...

[skydragoness]

technically, cylinder de-activation isn't as efficient as the other methods for increasing fuel economy. You still more or less suck in the same amount of air, and therefore burn more or less the same amount of fuel. You might save a tiny bit of "work" done by the engine by leaving the valves open, but at the end of the day, Engineers are working more on increasing an engine's efficiency of turning a fuel into energy that propels you forward. Current internal combustion engines are getting better, but still really don't crack 30% efficiency.

A 6 stroke diesel with a water injection (second power stroke) would be MASSIVE gains in efficiency. You'd be turning all that wasted heat energy that we currently circulate through a heat exchanger known as a radiator into power. Exhaust gas temperatures would be much lower too.

Realistically, ALL belt driven accessories can be driven off turbines in the exhaust system.

Direct injection is good, but the internal combustion engine still needs an evolutionary leap in the form of gaining another ~30% efficiency. Nuclear power for that matter does as well. Bleeding off enriched radioactive materials to boil water and spin a turbine at 20% system efficiency is kinda dumb if you ask me.

[MinisterofDOOM]

You still more or less suck in the same amount of air, and therefore burn more or less the same amount of fuel.

You don't need to suck in air if you leave valves closed. Close them halfway through a fuel-free intake cycle and you benefit from some compression "rebound" on the downstroke and some vacuum on the upstroke. Don't reopen exhaust or intake valves for that cylinder until it needs to start firing again. Of course you never get back the work you put in, but at least you're getting back more than none in this case.

Even ignoring cylinder deactivation, I still don't see why less displacement with the same amount of cylinders wouldn't be beneficial in reducing operating RPM (somewhat countered by more cylinders firing per rotation, of course), broadening power curves, and generally returning a more refined experience while still reducing fuel consumption.

I really just hate 4-cylinder motors. I hate how they sound, I hate how they feel, I hate how they deliver power, I hate that you have to choose torque or responsiveness and can't get both as with a 6 or an 8. I really cannot stand them. Even my favorite four-cylinders, like the KA or the Pinto 2.3, have major knocks against them (the KA sounds like wet farts, the Pinto uses 2 plugs per cylinder and isn't very efficient). You just don't have to make those sacrifices with V8s. You get smooth, you get torque, you get high redlines, you get power EVERYFRIGGINWHERE...you can't lose. The ONLY place you do lose is efficiency, and I'd rather work on improving that ONE WEAKNESS than just say "to Hell with it" and start throwing boosted fours in everything. Boost makes power, but it doesn't compensate for everything else fours do wrong. Four-cylinder motors have come a long way over the past 5 years alone. But I'm not ready to abandon every other engine format out there for a few miles per gallon under ideal circumstances.

[raremotive]

A 6 stroke diesel with a water injection (second power stroke) would be MASSIVE gains in efficiency. You'd be turning all that wasted heat energy that we currently circulate through a heat exchanger known as a radiator into power. Exhaust gas temperatures would be much lower too.

Realistically, ALL belt driven accessories can be driven off turbines in the exhaust system.

Direct injection is good, but the internal combustion engine still needs an evolutionary leap in the form of gaining another ~30% efficiency.

I have bunch of random stuff in mind.

I have yet to see anything more about the diesel 6-stroke since 3 years ago when I read about Carrillo's progress on it.

The other method was a gas Stirling engine, but it's very complicated and heavy. But it would turn exhaust and coolant energy to mechanical motion.

Other leaps of technology has been drive by wire, it actually uses the valves to throttle the engine instead of the throttle body or overall VE is improved. Pumping losses are reduced and throttle response is improved.

Direction injection is very good, and CR can has been bumped up higher up to 13:1+.

I actually would like to see a thermo-diode for an alternator off the exhaust system. I need to somehow make a few myself.

I do agree with the downsizing, but I don't see why can't they do a 2 to 3 liter v-6 with a pair of turbos. For regular driving 2-3 liter economy and for fun and power just push the pedal to crank up the boost. But this would be for a sedan. A compact car ie Ford Focus can see a 1 liter 4 cylinder only paired with a nice healthy turbo. The concept is pretty much what Ford has done for their F-150s.. instead of a 5.4 V-8... smaller 3.6L v-6 with a pair of turbos. Economy when you are cruising and power when you need it.

And last on the list is CVT, If you look at a BSFC map of an engine, if we could hold the RPM at where the least fuel consumption and change the gear ratios correctly it can roughly load the engine accordingly. In theory it would work, but I have no experience with how manufactures use their CVT's.

[MinisterofDOOM]

The concept is pretty much what Ford has done for their F-150s.. instead of a 5.4 V-8... smaller 3.6L v-6 with a pair of turbos. Economy when you are cruising and power when you need it.

The real world has shown that Ecoboost offers NO economy improvements. In fact, it's worse than the old 5.4, which was already a gas guzzler. In the Taurus, real world combined MPG is 16. Atrocious. And in 4x5 F150 it's about 14, which is no better than any half-ton V8--actually worse than some. I will say this again. And again and again if necessary: BOOST IS NOT THE ANSWER TO FUEL ECONOMY. You're still injecting more fuel along with more air. Yes, IF you stay out of the throttle and IF you never need power, and IF you've got a transmission geared correctly and IF you never get on boost, you'll get an improvement. But those things will never happen. It pisses me off to hear Ford, and the EPA, and everyone else talking about 22mpg this and that, when the truth is nothing of the sort. We're standing around bragging about our broken solutions instead of WORKING ON REAL ONES. Snake oil doesn't cure s***, and promising people otherwise is unethical and dangerous.

The same is being seen in the Sonata turbo, where 22-25 combined is the real world mark. Hardly exceptional and certainly within the realm of V6 capability.

The point I'm getting at through all of this is that neither of these compromises turned out to be worth the sacrifice. The end yield is a handful of MPG at best...maybe 5 max...on the part of the Sonata and zero and even NEGATIVE on the part of Ecoboost V6. Even the Ecoboost 4 in the new pansy-a** unibody Exploder has proven to barely "break even". None of it is worth it.
You can keep your 5mpg. I'll keep my V8 and my smile.

[raremotive]

The concept is pretty much what Ford has done for their F-150s.. instead of a 5.4 V-8... smaller 3.6L v-6 with a pair of turbos. Economy when you are cruising and power when you need it.

The real world has shown that Ecoboost offers NO economy improvements. In fact, it's worse than the old 5.4, which was already a gas guzzler. In the Taurus, real world combined MPG is 16. Atrocious. And in 4x5 F150 it's about 14, which is no better than any half-ton V8--actually worse than some. I will say this again. And again and again if necessary: BOOST IS NOT THE ANSWER TO FUEL ECONOMY. You're still injecting more fuel along with more air. Yes, IF you stay out of the throttle and IF you never need power, and IF you've got a transmission geared correctly and IF you never get on boost, you'll get an improvement.

I never said boost was for economy.

It's obvious boost is for power. Power means more fuel. But you should not boosting when you are unloaded and cruising, so you get the economy from the smaller engine. Less air, less fuel. Why Turbo V-6? So you can get the power as a large displacement V-8 (because of the turbos), economy of the v-6 (because you shouldn't be boosting during normal cruising).

Japanese been doing it for decades, one example is the turbo 2-2.5L Turbo RB motors, they got 30+ high way miles. But have the power of super car v-8 when you want it. I don't know what your grudge with ford, but in the real world... eco's 25 mpg is an improvement when compared with dated 5.4's 18 mpg. Highway miles as most truck users use. And boost when they need power.

I do think manufacturers can do a better job at mapping the wastegate, because at 60 mph would be boosting around 5 psi, be nice if it was set up like your idea like turn on the cylinders, cept..no boost until the pedal is pressed in enough or flip a economy switch to let boost off.

Keep your V-8. I prefer small displacement turbo'd inline-6's, 120 crank notes are music to my ears...but I can't have my way for latest and greatest ... without going with an BMW...

[MinisterofDOOM]

I never said boost was for economy.

That was directed at Ford, Hyundai, and everyone else out there, not you.

I do agree that boost has a purpose, especially when combined with other tech we've discussed in this thread. Your idea of active boost management is exactly the kind of stuff I want to see on little 6s and 8s. Especially if you can bypass the exhaust turbine altogether when not needing boost. Imagine a 3 liter V8 with two small turbos and maybe even a bigger electric one, all of which can be completely bypassed or enabled on-demand. I agree with boost as a shortcut to power, but not as an economy tool.

I don't know what your grudge with ford, but in the real world... eco's 25 mpg is an improvement when compared with dated 5.4's 18 mpg.

I have no grudge with Ford. Hell, I've owned two Fords. I love a lot of what Ford is doing these days. I do NOT like Ecoboost.

but in the real world... eco's 25 mpg is an improvement when compared with dated 5.4's 18 mpg.

As I've just said, there is no 25mpg in the real world. Combined is 14. Which is V8 league fuel economy. Read any review, or look for ford owners forums. NO ONE is getting EPA numbers out of Ecoboost, except (apparently) the EPA. Every single magazine under the sun averaged 16mpg in their SHO Taurus. And every owner I've met says the same thing. F150 forums are rife with people complaining about 14mpg combined fuel economy.
There is no 25mpg. NOT in the "real world."

[PapaSmurf2k3]

I would think theoretically a smaller displacement high cylinder vehicle would have better control over timing and flame propagation than a larger cylinder (think smaller combustion chamber)... although I bet the cylinder head gets crowded as the bore goes down (spark plugs are the same size no matter what). The valves would have to shrink quite a bit.

[C-Kwik]

You don't need to suck in air if you leave valves closed. Close them halfway through a fuel-free intake cycle and you benefit from some compression "rebound" on the downstroke and some vacuum on the upstroke. Don't reopen exhaust or intake valves for that cylinder until it needs to start firing again. Of course you never get back the work you put in, but at least you're getting back more than none in this case.

I believe what he was getting at is that power is generally a function of airflow. So for a given amount of power needed, whether its 4 cylinders or 8 cylinders, its still flowing roughly the same amount of air. The big benefit of cylinder deactivation is not that less cylinders are firing. Its that with only half the cylinders sucking in air, the throttle needs to be open further, which translates to less resistance to flow. The engine works less to suck in the air.

Even ignoring cylinder deactivation, I still don't see why less displacement with the same amount of cylinders wouldn't be beneficial in reducing operating RPM (somewhat countered by more cylinders firing per rotation, of course), broadening power curves, and generally returning a more refined experience while still reducing fuel consumption.

Depends on the overall displacement. There are optimum ranges for piston bores and strokes (and the volumes they create) that tend to optimize power and efficiency. A 2.0L V8 may yield a smooth motor, but may not be as efficient or powerful as a 2.0L 4-cylinder. And even if it was, it would have to have enough benefit of all the extra parts to justify the difference in cost.

I really just hate 4-cylinder motors. I hate how they sound, I hate how they feel, I hate how they deliver power, I hate that you have to choose torque or responsiveness and can't get both as with a 6 or an 8. I really cannot stand them. Even my favorite four-cylinders, like the KA or the Pinto 2.3, have major knocks against them (the KA sounds like wet farts, the Pinto uses 2 plugs per cylinder and isn't very efficient).

While I do prefer more cylinders to less, torque is generally a function of displacement. And generally, 4 cylinder motors aren't going to be all that big. Responsiveness is also not exclusive to motors with more cylinders, nor is it a trait inherent to them.

You just don't have to make those sacrifices with V8s. You get smooth, you get torque, you get high redlines, you get power EVERYFRIGGINWHERE...you can't lose. The ONLY place you do lose is efficiency, and I'd rather work on improving that ONE WEAKNESS than just say "to Hell with it" and start throwing boosted fours in everything. Boost makes power, but it doesn't compensate for everything else fours do wrong. Four-cylinder motors have come a long way over the past 5 years alone. But I'm not ready to abandon every other engine format out there for a few miles per gallon under ideal circumstances.

V8's are inherently smooth, but 4 cylinders can still be made to be smooth. Its a matter of damping or cancelling the vibrations. And its not like vibrations are ignored in V6 or V8 motors. Aside from that, there isn't any reason a 4 cylinder can't have good torque (relative) or high redlines. Plenty of 2-3 and 4 cylinder motors in motorcycles will easily outrev anything but F1 cars. A lot of modern turbo fours have achieved good low-end torque and pretty broad/flat torque curves. Not saying its perfect, but manufacturers are generally going to follow market trends. The buzz you say you hear about gas mileage definitely has manufacturers looking for solutions. So if only a handful of people don't care a lick about the cost of fuel, do you think its worth it for a manufacturer to build to please the relatively small group or try to hit a broader target. Other than niche manufactures that's unlikely.

I actually would like to see a thermo-diode for an alternator off the exhaust system. I need to somehow make a few myself.

Check the January issue of Car and Driver. They have a picture of a semi-conductor based generator that is powered by exhaust heat.

It's obvious boost is for power. Power means more fuel. But you should not boosting when you are unloaded and cruising, so you get the economy from the smaller engine. Less air, less fuel. Why Turbo V-6? So you can get the power as a large displacement V-8 (because of the turbos), economy of the v-6 (because you shouldn't be boosting during normal cruising).

Its actually not that obvious. There is no reason a turbocharger can't be used to increase efficiency. Turbos do tend to be able to work over a relatively large range of airflow so it would generally have the ability to increase power output, but turbos are not limited to increasing power. One way to try and see this is to think of a turbo that uses the exhaust energy to reduce pumping losses (rather than increasing power). Using a turbo could allow one to get the same power at a lower RPM and if the turbo is sized to optimize efficiency at this RPM, and load, it can increase efficiency. Its likely manufactures already do this to some extent.

It seems silly to me that we scale cylinder count with displacement. Twenty years ago cars had 3 liter V6s and 5 liter V8s. Now everything has 3.5 liter V6s and 6 liter V8s. But our 3.something-liter V6s are making more power than those 5 liter V8s did 20 years ago, and we're STILL increasing displacement. If we've come that far...from 160hp out of 3 liters (53 hp/liter) to 330 out of 3.6 (91hp/liter) why the Hell haven't we started scaling SIZE back, so we're looking at 200hp out of 2.2 liters? Or 250hp out of 2.5 liters? Or...etc, etc.

Problem is cylinder size does matter. They can effect power and efficiency. Small cylinders will have a high volume to surface area ratio. There is going to be more heat loss to the engine. Bore and strokes of gasoline engines have certain ranges where things tend to work more optimally. Combustion processes are complicated such that you can't just scale a motor and expect great results. Consider going in the other direction and build a motor with a huge piston. Flame front speeds could be a problem if you try and rev it high. There are a lot of physics at play. Hell, even cost benefit could be a factor in choosing bore and stroke sizes. I don't claim to know them all, but I do know its not as simple as you make it sound. Bottom line is there are many compromises that are made to fit within a certain set of design constraints in addition to the scientific constraints.

[nissangirl74]

Keep talking guys. I'm taking notes and learning stuffs.

[JaredM]

Thorium power? 35,000miles+ per gram.

[raremotive]

but in the real world... eco's 25 mpg is an improvement when compared with dated 5.4's 18 mpg.

As I've just said, there is no 25mpg in the real world. Combined is 14. Which is V8 league fuel economy. Read any review, or look for ford owners forums. NO ONE is getting EPA numbers out of Ecoboost, except (apparently) the EPA. Every single magazine under the sun averaged 16mpg in their SHO Taurus. And every owner I've met says the same thing. F150 forums are rife with people complaining about 14mpg combined fuel economy.
There is no 25mpg. NOT in the "real world."

If you read the next sentence, highway miles, not average or combined. I also read and seen first hand 25 mpg highway.

Lots of people need to learn to use their right foot better to get their city MPG higher. Boost is addicting, not need to be a psychiatrist to diagnose that. Also, all you have to do is watch traffic it's like a race to the next stop light.

It's obvious boost is for power. Power means more fuel. But you should not boosting when you are unloaded and cruising, so you get the economy from the smaller engine. Less air, less fuel. Why Turbo V-6? So you can get the power as a large displacement V-8 (because of the turbos), economy of the v-6 (because you shouldn't be boosting during normal cruising).

Its actually not that obvious. There is no reason a turbocharger can't be used to increase efficiency. Turbos do tend to be able to work over a relatively large range of airflow so it would generally have the ability to increase power output, but turbos are not limited to increasing power. One way to try and see this is to think of a turbo that uses the exhaust energy to reduce pumping losses (rather than increasing power). Using a turbo could allow one to get the same power at a lower RPM and if the turbo is sized to optimize efficiency at this RPM, and load, it can increase efficiency. Its likely manufactures already do this to some extent.

Very true. Pumping losses are high during part throttle operation. If a turbo can use wasted energy with minor back-pressure impact to pump air pressure in so that the engine doesn't have to suck it in there would be an improvement in efficiency.

[frapjap]

I'm surprised that no one has brought up the Mazda K series engines of the early 90's, which were among the smallest displacement for the most cylinders. They were impressive little pumpers with 4 valves per cylinder making anywhere from 130-200hp in the MX-3 and MX-6, a 1.8l V6 and a 2.5l V6, respectively. The smaller 1.8l even had a 7k rpm redline. The 2.5 wasn't a very high rev engine, but the torque curves and power delivery of both were extremely fluid. In the 2.5l engine, they had just as much torque as they did hp. I agree with MOD up there- 1.8l and 2.4l 4 cylinders that aren't always as smooth or torquey as the small displacement v6's. Even cars like the Probe, 626, and Millenia eventually adopted use of the engine.
Unfortunately, most of these cars eventually fell apart due to age and abuse, or had poor maintenance causing timing belt issues.

Given the opportunity, I'd love to get a hold of an MX-3 in good condition to use for the track. Very well designed chassis, engine, and suspension. The only real downside to the engine is that it was almost always facing the wrong direction.

[Bubba1]

There's an aspect to vehicle efficiency I think many of us are leaving out from this discussion, and that's weight. Most new cars available for purchase in the US are saddled with so much cr@p required by our government's safety/emissions regulations, cr@p installed to lessen the chance of lawsuits, or laden with so many luxury cr@p, that American driver can't seem to can't live without or are too lazy to do without, all create weight which works against efficiency. Look at the weight of a 1st gen Civic versus a new one. It's crazy.

Unfortunately most car makers have chosen to throw even more technology at these vehicles, like hybrid technology, to coax up "efficiency", which is not the only answer. All they've accomplished is make the vehicle more complicated and heavy and therefore more things to break and more costly to fix.

Ariel and Lotus both demonstrated what's possible with modest motors, just by keeping it simple and reducing weight.

As far as gasoline V8's are concerned, I've always liked the growl, torque and relative smoothness of a V8. I actually like Ferrari V12's even more, but IMHO more cylinders are NOT a requirement for a fun or fast or efficient driving experience.

[MinisterofDOOM]

Absolutely agreed, Bubba. I'm sick of seeing curb weights climb while displacement falls. The new Accord gets a gutless, torqueless 2.4 liter I4 in the base model, but weighs 3400 lb (or 3700lb in Crosstour form) which are both INSANE. The Taurus weighs between 4000 and 4500. It's ridiculous.
You need power to move weight. Insufficient power becomes inefficient.

I'm surprised that no one has brought up the Mazda K series engines of the early 90's, which were among the smallest displacement for the most cylinders.)

I'm ashamed I forgot about them because I'm a fan myself. I LOVE the miller-cycle 2.3 V6. I loved the Millenia it came in, too. I've always rather liked the MX3 as well, but I never realized it had a 1.8 liter K series V6. That's friggin' awesome. The 2.5 K series was in the MX6, another of my favorite Mazdas, along with it's hideously ugly Ford twin the analProbe.

[C-Kwik]

There's an aspect to vehicle efficiency I think many of us are leaving out from this discussion, and that's weight. Most new cars available for purchase in the US are saddled with so much cr@p required by our government's safety/emissions regulations, cr@p installed to lessen the chance of lawsuits, or laden with so many luxury cr@p, that American driver can't seem to can't live without or are too lazy to do without, all create weight which works against efficiency. Look at the weight of a 1st gen Civic versus a new one. It's crazy.

If left unabated, air quality, especially in higher population density areas would be quite bad. Its a necessary evil. But how much do you think the emissions parts on a car actually weigh? I can't imagine it being significant enough to make a huge impact on fuel efficiency. As for safety, I suspect it would increase a cars weigh more than emissions, but considering how much safer cars are today, I can't say its not worth the benefits. Not to mention some of that weight also has some benefit where chassis stiffness was increased. That said, consider that 1500lb Civic with only 50HP got something like 40 mpg. The new Civic (non-SI) has nearly that while having a much nicer set of options, more room, more power and less emissions. Not saying weight is a good thing, but its not always a bad thing either.

Unfortunately most car makers have chosen to throw even more technology at these vehicles, like hybrid technology, to coax up "efficiency", which is not the only answer. All they've accomplished is make the vehicle more complicated and heavy and therefore more things to break and more costly to fix.

Hybrid technology is a paradigm shift in fuel economy. The extra weight is more than made up for by its ability to recover and reuse energy that was extracted from fuel by the engine. There are other ways to increase efficiency, but none can make such a large leap in efficiency. And increases in engine efficiencies would still benefit hybrids. Weight does suck for vehicle dynamics, but most people shopping for hybrids aren't looking for sporty cars.

Ariel and Lotus both demonstrated what's possible with modest motors, just by keeping it simple and reducing weight.

Right, because those are practical and cheap. /sarcasm. Surely, when there are less constraints put in place to achieve a specific task, the solution is easier. But when you have a lot more constraints with a much broader set of goals, more compromise is needed.

The new Accord gets a gutless, torqueless 2.4 liter I4 in the base model, but weighs 3400 lb (or 3700lb in Crosstour form) which are both INSANE. The Taurus weighs between 4000 and 4500. It's ridiculous.
You need power to move weight. Insufficient power becomes inefficient.

The new Accord has a 2.4L motor that makes more torque than the KA did (albeit by a measly one tick; not accounting for the changes in SAE testing procedures) but has more HP and better fuel efficiency than the lighter 240sx did. If one wants more torque and cylinders, there is a V6 option. But its likely more people make compromises and get the cheaper, more economical motor. Life just isn't always ideal.

[MinisterofDOOM]

The new Accord has a 2.4L motor that makes more torque than the KA did (albeit by a measly one tick; not accounting for the changes in SAE testing procedures) but has more HP and better fuel efficiency than the lighter 240sx did. If one wants more torque and cylinders, there is a V6 option. But its likely more people make compromises and get the cheaper, more economical motor. Life just isn't always ideal.

More peak torque. The KA's torque curve was flatter than a Lexus-owner's EKG. The K24Z3 is a Honda motor, so its graph is shaped like a crackhead's hypodermic syringe.

[C-Kwik]

Are you kidding? All the KA had was low end and mid-range torque. Past 5000, the torque dropped off sharply. Not what I consider flat. Honda has done a pretty good job in maintaining a flat curve through redline. They probably give up a little to the KA at under 2000 RPM, but after that, the KA isn't anything that impressive. What Honda VTEC motors have gotten a bad rep from is purely from the relative torque. What I mean by that is, for a given peak HP, the torque appears quite small. One famous comparison was the KA vs the B16 from the Civic Si. The Civic has slightly higher HP at 160. The KA has gobs more torque (111 vs 160). But given the Civic's much higher redline, they can (and to some extent probably do) use a lower gear ratio and make use of leverage to put more torque than the published numbers suggest, to the ground. If we assumed both motors redlined at the same vehicle speeds in each gear, the SI motor would put something much more comparable to the 240 down to the ground (about 85% of it). But here is the real kicker. The civic maintains at least 80% of its peak torque from at least 2000 RPM through redline. The KA, only from at least 2K to maybe 5300 RPM. I say at least 2K in both cases as the dyno chart I'm looking at doesn't really go below that.

That said, I can't locate any of the 177HP K24 dynos, but the 201HP version I found for a TSX maintains more than 80% of its peak torque through almost the entire dyno run. I can't speak to the 177HP version directly, but my speculation is that without needing to try and balance more peak power on the hotter cam profile, they can easily use the extra breathing room to make for a very flexible torque curve. Honda engines are not inherently peaky. The KA's torque curve actually looks peaky compared to a lot of VTEC motors. To be clear, I'm in no way knocking on the KA. Its some 20 years old in design so one would expect improvements. But modern engines generally perform better than old engines.