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When the last fuel crisis poleaxed the country in the early Eighties, automakers responded by downsizing vehicles and their engines, reducing horsepower, and making every possible change to extract the maximum mileage from a gallon of fuel. The result was efficient cars that were among the dullest ever inflicted on their suffering buyers.

With today's much more sophisticated technology, it should be possible to boost fuel economy substantially without making major compromises in performance or driving satisfaction. In keeping with the fuel-economy theme of this issue, I've brainstormed my notion of the perfect sports sedan for these times. To make it easier to understand my thinking, it makes sense to start with an already efficient car, theC/D perennial 10Best-favorite BMW 3-series, a car that has useful space for four people and drives very well.

A base 328i sedan weighs 3340 pounds. Because weight degrades both performance and fuel efficiency, the first step is to shed some, with a goal of an even 3000 pounds.

BMW is already using carbon-fiber roof panels on some M models. Eliminating the sunroof and making the roof from carbon fiber would rid the car of roughly 40 pounds. A hood and a trunklid of the same material would save another 25 pounds. Carbon-fiber front fenders might lop off 30 pounds, with four similar door skins taking off another 40 pounds. That adds up to 135 pounds without changing the basic structure of the car at all.

Titanium is another glamorously high-tech material that could shave weight. Replacing the four steel suspension springs with titanium equivalents might be worth 50 pounds. Titanium mufflers and exhaust pipes could account for another 30 pounds, bringing titanium's diet contribution to 80 pounds.

Keep Reading: A Sports Sedan for the Next Decade: 3000 Pounds, 300 HP, 30 MPG, 3 Liters. - Column