Crazy. I'd like to read more about this but am to lazy to google. How'd you know this?

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the main reason is that friction in an engine grows exponetionally as engine revs climb. so an engine is loosing 4x as much power to friction at 4k rpm compared to 2k rpm or 8x at 8k rpm. the amount of power it takes to get a given mass up to a given speed is fixed. a small engine has to rev higher to produce that power but a larger engine doesnt have to work as hard. a good example is comparing a honda s2000 to a corvette zo6. the honda has a 2 liter (depending on the year) that revs really high while the zo6 has a 7 liter pushrod v8. even though the corvetter weighs almost 300 lbs more, it is still more efficient because it can cruise at 65 mph while the engine is barely turning over.

this is the same reason that these new turbo+direct inject+VVT engines are able to be more efficient and more powerful. the synergy of those technologies makes engines that are small but behave like large engines. compare the torque curve and mpg of a GTI to a civic si. they both make 200hp but one does it at significantally lower rpm. the gti holds over 180 tq through most of its rev range and the civic never gets close to that number.

a smaller engine is only going to be more efficient in a smaller car. if you put an engine in that is too small, mpg will suffer.

if you want to get the best possible mpg out of your car, floor it at low rpm. that is when the engine is operation at its highest efficiency.

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No. The losses are not exponential. Road cars do not run the oil sump in a vacuum. The thermal efficiency picks up once you get past 10% load.
http://www.techno-fandom.org/~hobbit/cars/prius-curves.gif
The BSFC minima is roughly in the middle of the engine speed range.
http://www.worldcarfans.com/photos.cfm/photoid/3060316.002/pageview/photo/photo/1027/size/large/country/jcf/lexus/lexus-rx-350
and neither the S2000 or Z06 has EGR (internal or external) or variable valve timing.
It is about 'right' sizing the displacement. Say something like a Navigator. Pick your size V12: 3 liters 70mm bore x 65mm stroke, 6 liter 85mmx88stroke, 9 liter 100x95. They will all move the truck, you just pick how much engine size to how much you will be using.

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ok, so it is slightly simplistic to say that friction rises exponentially with rpm. some sources of friction do while others are more linear or even drop.

there are hundreds of places an engine looses power and the oil sump is just one. the largest source of friction is the air being moved through the engine. different engines are tuned to move air efficiently at different rpm ranges. but, as a rule of thumb, the faster the air is moving, the more turbulent the flow.

obviously, there is a certain rpm range for IC engines, so it is going to be more efficient above a certain threshold where it is not designed to operate. for example, 6th gear at 5 mph is not efficient. but as a rule of thumb, the lower gearing that you can have with a torquier engine partially offsets the losses a larger engine has when accelerating its larger, heavier drivetrain. also, lower gearing means that some of the drivetrain has a smaller change in rotational velocity (it takes less power to spin a clutch and flywheel from 1500 rpm to 3000 rpm than it does to go from 2000 rpm to 5000 rpm to accomplish the same change in wheel speed). so clearly there are offsetting factors with their own offsetting factors here.

using the IC part of the prius drivetrain is not very representative of automobile engines as a whole.

of course there are situations where a larger engine is less efficient than a smaller one but if the larger engine where set up to make the same amount of power at lower rpm, all else being equal,(which it never is) it would be more efficient. of course a torquier engine needs a beefed up transmission, drive shaft, wheels/tires ect. all of which is reciprocating weight.

im not sure where you are going with the EGR thing. but since neither of the vehicles has them it is null for the purposes of the comparison. the s2000 does have variable valve timing and lift, the switchover happens at 5850 rpm on the 2 liter. that is supposedly another fuel saving technology and only further stregnths the point i was trying to make. both are high performance engines that breath extremely well and demonstrate the current limits of technology for their respective schools of thought about producing power in a small package. the ls7 is a larger engine, with twice as many cyl, in a heavier car, without variable valve control, producing over twice as much power and it still comes out ahead. oh and by they way, the two engines are pretty close in terms of cost to manufacture...

i hear people complaining that mileage has stayed the same while average 0-60 and hp has gone up dramatically. as if global warming is horsepowers fault. i am trying to debunk the myth that if only GM would put a 1.5 liter 4 cyl in everything, then all cars would get 40 mpg. its just not the case. a large car needs a large engine. a 2 liter revving at twice the rpm is not a suitable substitute for a 4 liter. just like a 4 liter at half throttle is not the as efficient as a 2 liter at full throttle. forcing everyone to just get used to less torque is not a solution and there is little correlation between faster 0-60 times and worse mileage but a direct correlation between heavier cars and lower mileage.

the three most important factors in fuel economy are
1 Weight
2 Weight
3 Aerodynamics
powertrain efficiency, where 99% of the money is being spent, is a distant 4th. we are well beyond the point of diminishing returns. we are now spending hundreds of dollars per car to raise efficiency a few tenths of one percent.

CARS ARE TOO BIG!!!

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So what would be a good rule of thumb.
1 liter of engine displacement for every 1000 lbs of weight?

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thats usually enough to get the job done

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1L per 1000 lbs is more than enough to get the job done, especially with the increases in hp/L we have seen.
Look at 4 cyl midsize sedans and you'll see something closer to 0.6-0.7L/1K lb. Probably around 0.5-0.75L/1K lb is where you are going to see the best economy if you are willing to give up a little acceleration.

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its really the torque that you need to look at. 50 lbs/ft per 1000 lbs is fine for a vehicle that is optimized for economy. also, its not peak torque that is important but the average torque that the engine is making through its used rpm range. 150 tq at 6k rpm sounds fine for a midsized sedan but if its only 80-100 in the lower rev range then mpg will suffer.

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i agree !

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The new xB might as well be badged "Highlander," and the real '08 Highlander ought to be the Sequoia.

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My wife has a BRIGHT green xB, and she loves it. She calls it the green toaster. When I was recently in the truck market, and we saw the new ones, and were completely disappointed. Its like Toyota completely missed the whole point of what the original car was about. Small, not fast but fast enough, lots of room without "being" huge, good gas mileage, and cheap. Plus the fact its seems like they created a blind spot, instead of the usual fixing of a blind spot.

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No. The current RAV4 is almost as heavy as the outgoing Highlander.
http://pressroom.toyota.com/presstxt/2007toyotakit/2007RAV4_s.pdf
http://pressroom.toyota.com/presstxt/2007toyotakit/2007Highlander_s.pdf
and the RAV4 has a good rear suspension, no struts like the highlander.

But this is the new paradigm. If you want the same weight, you need to move downmarket. The yaris replacing the corolla, the fit taking the civic's spot.

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Your going to have to look up the "Smart car" crash tests. Bigger is not always safer.

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Way to miss my point, Barney. The Smart is a NEW design. I'm talking about new car safety vs. lighter, unsafe cars of 15 years ago.

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