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We will use this section to provide you with basic math formulas that can be directly related to vehicles and performance. These are such simple things as computing the area of a circle or converting cubic inches to cubic centimeters.
Circumference of a Circle Diameter of a Circle Radius of a Circle Area of a Circle Volume of a Cylinder Convert Volume Time per Degree of Rotation
Knowing the circumference of a circle can be very helpful. Especially in relation to tires. If you know the diameter of a specific tire, you can compute the circumference.
Note that this is an "ideal" circumference. It does not take into consideration the flattened contact patch of the tire.
Conversely, if you measure the circumference of a circle (a tire), you can compute the diameter in the same way. (P.S. A good way to measure a tire's circumference is using a seamstress' tape).
Note that this is an "ideal" diameter. It does not take into consideration the flattened contact patch of the tire.
Knowing the radius of a circle can also be helpful. The radius is simply one half (1/2) the diameter.
Note that this is an "ideal" radius. It does not take into consideration the flattened contact patch of the tire.
Last but not least, you sometimes need to know the area of a circle. This is one component of computing the volume of a cylinder.
Knowing the volume of a cylinder can also be helpful. The volume of a cylinder is basically it's swept volume and also can be close to it's displacement.
Two other formulas that come in very handy are to convert from cubic centimeters to cubic inches and vice versa.
A very important basic math formula is how to compute the timing of movement of fluids. The results of this formula should then be used to against a known speed, such as the speed of sound, to compute how long a quantity takes to move per degree of crankshaft revolution.
For example, intake charge may move at the speed of sound, i.e. in an ideal medium around 1088 feet/second, while exhaust, which is hotter, will move faster, say around 1700 feet/second. Armed with this knowledge, and the length of your intake or exhaust track, you can compute how long a segment of intake or exhaust charge will take to enter or exit your system.
Notice I say "segment". You must take a "slice" of your intake or exhaust and track that. Then figure how many "slices" will enter or exit your system in the time alloted by valve timing and degrees of crankshaft rotation.
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Last revision : August 30, 2009
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