Book Excerpt: Performance Automotive Engine Math: For Street and Race Applications BASIC MATH AND SCIENCE
You can't do engine math without numbers. The numbers we use are measured with precision tools or, in some cases, they are assigned values for the purpose of brainstorming proposed modifications and theoretical results. Measurements are taken in what we all recognize as U.S. Customary units of measure such as feet, inches, pounds, and gallons; international SI or metric units such as millimiters, centimeters, and liters are also relevant because many of new cars use a combination of both. Once dimensions and other measurements are recorded they can be mathematically manipulated to tell us almost anything we want to know about our engines, including how they might perform and how we might modify them. Engine math deals with rod and stroke lengths, bearing diameters and clearances, cylinder volumes, bore/stroke ratios, piston weights and speeds, cylinder pressures, atmospheric temperature, and so on.
Engine displacement is the most common math calculation. Displacement is the size of volumetric capacity of an engine expressed in cubic inches, cubic centimeters, or liters. Here in America, we typically work in cubic inches while the rest of the world uses the metric system. I discuss appropriate conversions later in this chapter. Displacement is determined by a calculation involving the bore diameter and the stroke length times the number of cylinders. The result is the actual swept volume of each cylinder and the total swept volume of the engine assuming 100 percent volumetric efficiency. Please note here that the actual swept volume is not the total volume of each cylinder since it does not include the volume of the combustion space above the piston at top dead center (TDC). These separate volumes allow you to calculate the engine's compression ratio (described in Chapter 3).
Subject: Performance Automotive Engine Math, for street and racing applications. | ISBN-10: 1934709476 | ISBN-13: 9781934709474 | SA204