# How to Calculate Silencer Sizes

Written by ryan menezes
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An engine's exhaust silencer must suit that particular engine's noise requirements. It must also suit the rate of exhaust flow. Too small a silencer will insufficiently muffle an engine's exhaust pipe. Too large a silencer will magnify the engine's back pressure, hurting engine performance. Determine your silencer's size from the gas's flow area. A number of factors affect the flow area, including the gas's temperature, the back pressure, the gas flow rate and the target silencer pressure drop coefficient.

Skill level:
Easy

## Instructions

1. 1

Square the engine's gas flow rate, measured in cubic feet per minute. If, for instance, 3,000 cubic feet of gas flow per minute: 3,000 ^ 2 = 9,000,000.

2. 2

Multiply your answer by the pressure drop coefficient. If you engine has a pressure drop coefficient of 4.2: 90,000 * 4.2 = 37,800,000.

3. 3

Multiply by 530: 378,000 * 530 = 20,034,000,000.

4. 4

Add 460 to the exhaust gas's temperature, in degrees Fahrenheit. If the gas has a temperature of 593 degrees C: 1,100 + 460 = 1,560.

5. 5

Multiply by the engine's back pressure, measured in inches of water. If the back pressure is 20 inches of water: 1,560 * 20 = 31,200.

6. 6

7. 7

Divide 20,034,000,000 by 500,448,780,000 = 0.04.

8. 8

9. 9

10. 10

Find the square root of your answer: 0.064 ^ 0.5 = 0.253.

11. 11

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