Automotive Terms Explained
By Mac Demere/autoMedia.com
Demystifying Car Jargon -
"What's a carburetor?" My teenager's question shocked me. Didn't he learn anything from all that time he spends on car websites? Then it struck me: He was an infant when the last carbureted new car was sold in the U.S. To him, carburetors are ancient technology, like flintlock muskets and Windows 98. When something's dead, it's dead. Here are definitions for commonly used automotive terms that confused him (and probably a lot of others, too), and that everyone might like to understand.
Carburetors were the analog version of fuel injection. Carbs did a great job of mixing fuel and air to meet an engine's varying needs. They were relatively inexpensive and largely reliable. However, they were made extinct by computer-controlled electronic fuel injection, which allows engines to produce more power, better fuel mileage, and, most importantly, cleaner emissions. Carbs are still used in some non-automotive engines, such as lawn mowers, and are mandated in NASCAR.
Torque and Horsepower
Torque is a twisting or rotational force. No motion is required. Imagine trying to turn the pedals of a bicycle wedged in a bike rack with its rear tire held firmly to the asphalt: The pressure put on the pedals is torque. Torque is measured and expressed in pound-feet: If that bike's crank is one foot long (it's a really long crank) and my son stood on one pedal, that's 135 lb.-ft. of torque.
Horsepower is a calculation. The formula: engine revolutions per minute (rpm) multiplied by the torque at that engine speed, divided by 5,252. In most passenger-vehicle engines, torque nears its peak early and remains fairly constant until it falls away due to friction and the weight of the moving parts. Horsepower rises with engine speed and hits its peak when increasing rpm no longer offsets falling torque in the math formula.
Which is better—torque or horsepower—depends on what the vehicle is designed to do. Here are two extremes: Some 18-wheeler engines make about 1,300 lb.-ft. of torque at just 1,200 rpm, however they top out at only 300 horsepower near the engine's 2,100-rpm limit. Recent Formula 1 race engines are reported to approach 900 horsepower at a mind-boggling 19,000 rpm and have a torque peak of 500 lb.-ft. at around 14,000 rpm. Without radically modifying the clutch, the F1 engine couldn't move the 80,000-pound semi. The big-rig's diesel would make for a very slow F1 car, partially because it'll almost double the weight of the racecar.
In comparable passenger vehicles, an engine with more torque at lower rpm will provide better acceleration from slower speeds. It's a different story on the racetrack. Take two otherwise completely identical cars (weight, suspension, gearing, tires) to the dragstrip. Car T has an engine that makes more low-end torque, while Car H's engine builder traded low-rpm torque for more high-rpm horsepower. Car T will take an early lead, but the driver will have to shift to second gear sooner and, thus, lose the torque-multiplying effect of the lower gear. By the time Car T shifts to third (and maybe sooner), Car H will take the lead.
Here's another factor: Horsepower and torque reported by manufacturers are not exactly what every engine produces for its entire life. Production tolerances cause variations. Wear makes power rise and fall. But importantly, the marketing department has a huge impact on the numbers reported. Sometimes the actual horsepower is higher than advertised: Rev it a bit more and it'll yield more horsepower. Two years later the marketers will be able to tout the car's 10 additional horsepower, which was there all along.