Chapter 6 Engine Types and Classifi cations 125 Copyright by Goodheart-Willcox Co., Inc. engine compartment. An equal number of cylinders is needed in each bank. A V-type engine may have six, eight, ten, or twelve cylinders V-6 and V-8 are the most common. V-8 engines usually have a large displacement and can be found in performance cars, luxury cars, and light trucks. They are very powerful and idle very smoothly because there are four power strokes per crankshaft revolution. The V-6 engine is now one of the most popular con- figurations. It is small, compact, produces good power, and provides good fuel economy. V-6 engines are lightweight and offer a good balance between power and fuel economy. They can be found as standard or optional equipment on most midsized vehicles. W-Type Engine A W-type engine is similar to a V-type engine. It has two banks of cylinders, but the cylinder bores in each bank are stag- gered, Figure 6-1. This allows for a more compact engine. Opposed Engine An opposed engine, also termed “pancake engine,” has two banks of cylinders that lay flat or horizontal on each side of the crankshaft, Figure 6-1. This configuration is also called a “boxer engine” because the pistons in opposite banks move toward each other, like the fists of two boxers. An opposed cylinder arrangement is found in several makes of cars. An opposed 12-cylinder engine can be found in top-of-the-line Ferrari performance cars. Porsche also uses an opposed 6-cylinder engine in many of their high-perfor- mance sports cars. Subaru uses an opposed 4-cylinder engine in some of their four-wheel drive vehicles. The opposed design allows for a vehicle with a very low center of gravity because most of the weight of the engine is near ground. Lowering the center of gravity improves the cornering of the vehicle. An opposed engine has the dura- bility of an inline engine with the compact packaging of a V-type engine. In addition, the power strokes of the opposed cylinders tend to balance each other and reduce the thrust on the main bearings. Reducing this thrust also reduces the horsepower lost due to friction in the main bearings. One disadvantage of an opposed engine is that oil leaks are more difficult to prevent, especially around the valve covers. The valve covers lay sideways and oil tends to seep out of the bottom of the valve cover gaskets. With inline and V-type engine designs, the valve covers sit more upright and are less likely to leak oil. Number of Cylinders Car and light truck engines normally have either 4, 6, or 8 cylinders. A few engines, however, have 3, 5, 10, 12, or 16 cylinders. A greater number of cylinders generally increases engine smoothness and power. For instance, an 8-cylinder engine produces twice as many power strokes per crankshaft revolution as a 4-cylinder engine. This reduces power pulsa- tions and roughness (vibration), especially at idle. In turn, a 12-cylinder engine runs even more smoothly. Four-cylinder engines usually have inline or opposed configurations. Six-cylinder engines can have inline, opposed, or V-type configurations. Five-cylinder engines normally have an inline configuration. Eight-, ten-, and twelve-cylinder engines have a V-type configuration. Cylinder Numbering and Firing Order Cylinder numbers identify the cylinders, pistons, and connecting rods of the engine. Cylinder numbers can be cast into the intake manifold corresponding numbers are normally stamped into the sides of the connecting rods. Cylinder numbering varies with the engine design and cyl- inder arrangement. Look at Figure 6-2. It shows typical cylinder num- bers for V-8, V-6, inline 6-cylinder, and inline 4-cylinder engines. Four-cylinder engines are usually numbered 1-2-3-4 from the front to the rear. On V-type engines, you can normally tell the number one cylinder because it is located slightly ahead or in front of the front cylinder on the other side of the block. Engine manufacturers use cylinder numbers so the engine technician can make repairs and do tune-up operations. For example, when rebuilding an engine, pistons and rods must be returned to the cylinder from which they were removed. Also, you will need to know which is the number one cylinder so a timing light can be connected during a tune-up. The firing order is given in terms of the cylinder numbers. Firing order refers to the sequence in which com- bustion occurs in the engine. In other words, it is the order in which cylinders fire. The position of the crankshaft rod journals in relation to each other determines engine firing order. Two similar engines can have completely different firing orders. Always refer to a service manual to verify cylinder numbers and firing order. Both will vary by manufacturer. For example, some V-type engines have one bank that con- tains all odd-numbered cylinders (such as 1, 3, 5) and the other bank all even-numbered cylinders (such as 2, 4, 6). Or, the cylinders may be numbered in sequence (1, 2, 3) on one bank and then in sequence (4, 5, 6) on the other bank. Crankshaft Classification There are several different ways to classify an engine crankshaft. The most common are: • An inline crankshaft only has one connecting rod fastened to each rod journal, Figure 6-3.