Automotive Terms Explained
By Mac Demere/autoMedia.com
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.
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.
This is the engine's internal size: It's the pistons diameter multiplied by how far they travel on each stroke multiplied by the number of cylinders. It's expressed in cubic centimeters (6,000 cc), liters (6.0-liters) or cubic inches (366 ci). Everything else being equal, increasing displacement usually increases torque and horsepower. But if the increased displacement reduces the engine's rpm potential (bigger pistons are heavier), the rise in horsepower may be small.