Designing or building a car that exceeds 40 mpg is super simple. But would you drive it? That's what drives what car manufacturers offer.

Picture this-

RX-7 body. 1st gen or 2nd gen. you take your pic. Either way the drag coeffiecnt was around .29.

Now take a 1.0L 3 cylinder motor that in it's last version strapped to a non- aerodynamic Geo Metro got an honest 40 mpg. Update the motor with current electronics including real world direct injection (not the TBI it had) plus instead of SOHC, make it a DOHC. Now you've bumped the hp up 8-15 hp and increased the effieciency by leaps and bounds.

You might go 0-60 in 12 seconds or so, and with the lower drag, higher output motor, you could climb hills adaquetly.

Fuel economy would roughly be 45-50 mpg. You could offer a diesel option- the 3cyl that VW has tested in Europe that gets 70 mpg in the city.

BUT- would the masses buy it? Probably not. Why? Because the US is full of vein sob's. Your car is a status symbol and their attitude is "I wouldn't be caught dead driving that thing I don't care if it got 100mpg"

The issue has nothing do do with current vehicle weight, or electronics. The vehicle is 100% feasable, but it won't make manufacturers any money cause nobody will buy it.

The issue has nothing do do with current vehicle weight, or electronics. The vehicle is 100% feasable, but it won't make manufacturers any money cause nobody will buy it. 

Very true, there is no incentive to buy that car with the current cheap fuel prices. If fuel prices doubled, I might consider it (actually I wouldn't consider it, but plenty of people probably would).

I agree that the technology for 40 mpg cars is already here. Way back at the beginning of this thread I cited hybrid technology and ultralight composites.

The reason people wouldn't buy them is simply the cost. Hybrids cost more, and converting manufacturing facilities from working sheetmetal to creating composit panels would be expensive. Making parts from sheet steel and spot welding them when the production line is already set up to do that is far cheaper than converting the entire line.

In short, the bulk of the marketplace simply won't pay the extra price for high mileage vehicles. And in all honesty I'd rather see them begin to look for ways to REDUCE the price of new vehicles. Stop adding bells and whistles and come out with a modern, cheap, basic, usable mode of transportation. Before Tata invades the market with their rolling rubbish barrels.

I agree the U.S. market needs a good cheap basic vehicle. I don't know who will provide it, but I'm fairly certain that it won't be the "big 2.1" (they've been demoted again). It may well be Tata, I remember when we all laughed at toyota/honda.

It is about weight and safety, not technology. Our 1981 Toyota Starlet was EPA rated at 50 mpg at that time, and would get very close to that with two aboard. After replacing the original tires, which were designed for low rolling and wind resistance, with tires that would actually stop the car in a panic stop, our actual highway mileage, averaged on a cross-country trip with two adults and luggage, was 44 mpg. By the way, the rear wheel drive Starlet got better mileage than its front wheel drive twin, the Tercel. So much for the myth of FWD giving better mileage.

It was big enough to seat 4 and still carry significant luggage. With a 5-speed stick it would easily keep up with traffic and climb any hill at 60 mph. The bad news was that it weighted 1700 lbs, had no air bags and no safety cage around the passenger compartment. It was only a little safer than riding my motorcycle, and I brought my two newborns home from the hospital in that thing!

I drove it 275,000 miles with no engine repairs at all, and it looked good and ran perfectly when I sold it. But then, it was never in an accident...

I think the main reason 40+ MPG cars are so rare is that, until about a year ago, nobody much wanted them. When gas was cheap, no one wanted to be seen in an econobox. Now that high-mileage cars are in demand, I'm betting there will be lot more of them on offer.

Everyone should take a minute to reflect on how much has been accomplished in terms of engine efficiency in the last 50 years.

The first car I drove was a mid 1950s Ford with a V8 and a 2-speed automatic transmission. No A/C or power anything. It got 15 mpg. My next car was a 40 hp VW beetle. 0-60 in 30 seconds with a top speed of 80 mph. It got 33 mpg. Its replacement was another beetle, this one with with 53 hp. 0-60 time dropped to 18 seconds, but gas mileage dropped to 30 mpg. We have a late 1960s Corvair that my wife inherited from her father. 0-60 in about 12 seconds. 18 mpg.

The early 1970s were a disaster for engine performance because emissions limits preceded the technology to implement them efficiently. Cars began getting only 10 or 12 mpg. I briefly rented a 1975 Ford Maverick with a 6-cylinder engine and automatic transmission. It got 13.5 mpg.

By the late 1980s, manufacturers were beginning to develop the technology needed for engines that were both clean and efficient. We had a Honda Civic that was as fast as the Corvair yet got the same gas mileage as my first VW beetle.

Computerized engine control and fuel injection made a huge improvment in efficiency. We have a 1998 Subaru all-wheel-drive wagon that is bigger than the Civic and weighs 50% more, does 0-60 in 8-9 seconds and gets 24 mpg. Cars like the Honda Civic and Toyota Corolla, which meet current emissions and safety requirements, are as fast as our Subaru yet get the same gas mileage as my gutless, tin box beetle did 45 years ago.

Last fall, I bought an Infiniti G37S coupe. 0-60 time is 5-6 seconds and top speed is limited by an electronic governor to 155 mph. In the real world, it gets the same gas mileage as the Subaru! Compared to the previous version of the same engine, it has the advantage of continuously variable valve lift and timing. The next step is direct fuel injection into the cylinders as is used for diesels. This should yield another 10% improvement.

I think the next breakthrough will be camless electronically controlled intake and exhaust valves. No need for a throttle, the intake valve just closes when enough air has been sucked into the cylinder for the power needed. Without the engine having to suck air past a closed throttle, the pumping losses will go way down and idle fuel consumption should drop down to that of a diesel engine.
Variable cam timing kind of achieves a portion of this but still needs a throttle to control engine power.

I think the next breakthrough will be camless electronically controlled intake and exhaust valves. 

It's been tried...Several companies have been working on it for several years (first I heard about it was 15 years ago). The problem is reliability. They haven't been able to make it reliable enough. The simpler the system the more reliable it is

It's "Rocket Science" because a Saturn V rocket is both the Least and Most efficient vehicle. Three inches per gallon of fuel at lift off, Infinity MPG in space. (LOL)

As cited in other threads, my 1992 Honda Civic VX 4cyl 3 door (hatchback) drove great, was reliable, and got 39city/55 hwy (verified by me as driver), AND it went uphill in 4th gear (not necessarily in 5th/overdrive) AND it had AC that worked well. Yes it was small, light, low profile, but far superior mpg vs. current models with no hybrid magic. IMHO, supply and demand. If we as consumers demand more, we'll get it. Auto company administrators are only responsible to stockholders, i.e. money talks.

WHY NOT?

I have a 2002 saturn SL (the last year they made them). Basic car with A/C, 5spd, 4 door and the single cam 4cyl engine. I drive mixed highway and higher speed rural roads.. no real city driving. I consistently get 41mpg!

I paid $10,000 for the car NEW

I just passed the 100,000 mile mark with no major repairs necessary (just brakes, tune-up, etc.)

Its a crime that such a car is no longer available!!

Funny that you mention HHO, I just ran accross a web site yesterday that was singing the praises of Stan Meyer for his HHO dune buggy. The problem is that every website I found that says HHO works, also preaches about "mysterious murders" "stolen research files" and so on. Some of them even admit that no one has been able to duplicate his claims even following his own plans. Every reliable website I could find states that as a automotive fuel HHO is worthless because it takes more energy to create it then you get out of using it for fuel.