Origin of the Species
Two months ago I talked about multiple valves per cylinder, an old technology that enables modern small engines to produce more power and use less fuel. But there’s another piece to this puzzle of going faster on less gasoline, and it’s one that has always carried a certain mystique in the sports car world: the twin-cam engine.
Twin or dual overhead cams in automobile motors went hand in hand with three- or four-valve-per-cylinder engines in the early days of racing. The design was used in many sports cars of the 1950s and ‘60s but didn’t make it into the mass (read: economy car) market until the ‘70s.
Once again, the gas crunch and higher fuel-economy standards brought a pricey piece of engineering down from loftier heights.
Obviously there’s a loss of “economy” from the buyer’s standpoint, because two cams and twice as many valves cost more.
In return, far more precise valve timing is possible because one cam controls the intake and another the exhaust. The load and wear and tear are spread over more parts. At any given moment, less weight is being moved in the valve train, resulting in lower friction and less worn metal in the oil. Heat dissipation is better, and the lighter individual moving pieces are mostly quieter.
Honda takes this a step further and wrings extra ponies out of its VTEC engines by having the engine control unit (a.k.a. computer) change the valve timing depending on operating conditions.
The use of any twin-cam design, however, doesn’t come without trade-offs. The increased power is mostly at higher rpm, and low-end torque suffers. As the saying goes, the car is faster but not any quicker. And if you prefer to spend your time making power on the high end, you’ll lose the advantage of a quieter valve train.
But is all of this complexity really needed? For small engines, yes. For modern V-6 and V-8 engines, no. As long as power is the first order of the day, a V-8 push-rod engine with electronic fuel injection can get decent gas mileage for the power it produces.
Case in point: The Corvette LS1 gets 25 miles per gallon in the city with an automatic transmission while producing 345 horsepower. Significantly better fuel economy than ‘Vettes of the early ‘70s, and in what is considered a much better car.
Quite a few cars on the market today use a single overhead cam and are capable of adequate performance and good mileage.
The question of whether you need a twin- or single-cam engine comes down to the same criteria car buyers use to make their choices: How much power do you want? How much money do you have?
Who Is Dr. Gear Head?
First, like Dr. Science, he’s not a real doctor. That aside, he has driven and owned a variety of cars, from the horrid to the sublime. He’s also owned a few motorcycles. Gear Head prefers to work on his own cars unless the task is complicated. Having once rebuilt a blown VW Beetle engine only to blow out the rebuild, he limits his practice. The good doctor currently drives a late-model roadster and also owns an aging (read: slow) sport-utility.
Poser Product of the Month
Do you lust after those blue-tinged ion headlamps but can’t afford the lofty prices? If all you care about is the look, you can now buy self-adhesive tinted covers for your stock headlights that supposedly make them look like the real thing. Just hope they don’t melt from the heat. (I spotted this wandering around the Net. Didn’t care, didn’t bookmark the page, so please don’t ask where to get them.)
Do you know of a part or accessory that serves no real purpose? E-mail us with the details and we’ll consider it for inclusion next time.
Write Us
Do you have a comment, question or suggestion for Dr. Gear Head? Write to Dr. Gear Head, Business Section, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053. Or fax us at (213) 237-7837, or e-mail us at highway1@latimes.com.
