Automotive Terms Explained

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.

Camshaft
This is the device that opens valves to let the air/fuel mixture in and burned gasses out. On a camshaft are several egg-shaped lobes, one for each valve operated by that camshaft. A camshaft looks like a boiled-egg kabob assembled by someone who didn't care which way the small ends were pointing. When the camshaft is rotated, the more pointy end of the cam lobe pushes the valve open and the rounded end allows it to close. The cam lobe can work either directly on the valve stem or through a linkage. (An engine valve looks like a broken wine glass: The stem is intact but the bowl—the part that holds the fluid—is gone.)


Today, most cams are located on top of the engine above the cylinder head. These are overhead camshafts. If one camshaft operates both intake and exhaust valves, it's a single overhead camshaft (SOHC). If there are separate cams for intake and exhaust, it's a dual overhead camshaft (DOHC). A DOHC "V" engine has four cams: Two over each of its heads. Traditional American V-8s, called overhead valve (OHV) engines, have a single camshaft located in the valley of the "V." This lone camshaft works all the engine's valves through a system of rods and levers (called pushrods and rocker arms). The advantages of overhead cams are efficiency, precision, and the ability to more quickly reach higher engine speeds. Disadvantages include cost, complexity, and, with DOHC, weight.

V What?
Almost all of today's internal combustion auto engines come in two flavors: Inline and "V." Inline means the cylinders are in a straight row like dog food cans on a counter. "V" (commonly V-6, V-8, V-10) means the engine's cylinders are aligned like the letter V: The angle of the V can vary depending on a number of factors. Inline engines tend to be smoother and lighter. A "V" engine is usually shorter and slightly wider than an inline with the same number of cylinders.