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For years I've been hearing about fantastic carburetors that can give your car up to 200 mpg. But supposedly the automakers and Big Oil won't allow them to come to market because they'd wreck the industry. The people who tell you this are usually conspiracy buffs who offer it as an example of how the masses are duped by the Illuminati, so you have to be skeptical. But still I wonder: is the 200-mpg carburetor a complete fantasy, or does something like it actually exist? Do you have one on your car? --Mike Wells, Santa Barbara, California

Actually, Cecil has been thinking about trying the gas-saving strategy pioneered by legendary Straight Dope cartoonist Slug Signorino. Never one to miss a chance to economize, Slug makes it a practice to go only to places that are downhill from him, so he can just put the car in neutral and roll. Admittedly this system has its limitations. But all sorts of other energy-efficient technologies exist, none of which has exactly lacked for publicity or industry backing.

A recent survey in Technology Review listed ten experimental cars developed by seven major automakers that get highway mileage ranging from 71 to 110 mpg. A few years ago Renault trotted out a rig that it claimed got 121 mpg. I'm told the gas mileage record for motorcycles is about 400 mpg, and if you really want to go crazy, a GM subsidiary recently built a solar-powered prototype called Sunraycer that doesn't use any gas at all. Weighing only 400 pounds, it completed a 1,800-mile race at an average speed of over 40 mph. On the downside, it seats only one, has no trunk or luggage rack, and for that matter barely has room for a pair of fuzzy dice. But hey, life is full of trade-offs.

It's important to note that high mileage is never the result of a single miraculous component, such as a carburetor. Rather it's the sum of numerous small improvements. Among these are lightweight materials, low-friction tires, improved aerodynamics, flywheels to store and reuse energy now lost during braking, and "ultra-lean-burn" engines for more efficient city driving (already available in certain Toyotas sold in Europe). Another improvement used in some high-mileage prototypes is the continuously variable transmission: instead of clumsily shifting gears, the cars shift transmission ratios gradually, typically using an ingenious (and conceptually quite simple) arrangement of cone-shaped pulleys and belts. Soon to come, it's believed, are ceramic diesel engines using turbochargers and perhaps stratified-charge engines that combine the best features of gasoline and diesel technology. While 200 mpg is pushing it, the experts think 100 mpg cars are within range of current technology.

Sounds great, you say? Well, don't rush down to the auto showroom just yet. It may be years, if ever, before the new technology becomes widely available. That's not because the automakers are conspiring to withhold it, but rather because they doubt the public will buy it. People today are less concerned about energy efficiency, and for good reason: corrected for inflation, gasoline today costs less than it did in 1973. Fuel-efficient cars tend to be little cars, and the trend in recent years has been in the opposite direction (although no one foresees a return to the old boats of the 50s and 60s). The only reason gas mileage has improved at all in recent years has been government-mandated fuel-economy standards, and God knows the Reagan administration did everything it could to frustrate those. The superefficient cars now on the drawing boards don't figure to be cheap, and unless gas prices skyrocket, the fuel savings probably wouldn't cover the higher cost. Barring a sudden burst of altruism on the part of the car-buying public, you probably won't see ultrahigh-mileage cars for sale until we've had three consecutive greenhouse summers or we're down to the last two gallons of Arab oil.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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