Buyer Beware ...

Published cylinder head air flow figures are not equal. If you really want to compare apples to apples you can use the multipliers provided below to convert flow numbers to the industry standard of 28" of water. To use the chart below, simply find the "inches of water" that your flow figures were tested at in the left hand column. Then follow the line over to the right until you reach the
multiplier under the inches of water that you want to know the flow at.

Let's say that the flow numbers you were provided were by the tester using 10" of water on the flow bench, and you want to know what that flow would be at 28" of water. By the chart below, the test multiplier would be 1.67. Now, multiply your flow number by 1.67. (Look at the shading in the table below)
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FOR EXAMPLE: If you have 183 cfm flow at 10" of water. Multiply the 183 flow number by 1.67 and you find that you have 305.6 cfm at 28" of water.

183 x 1.67 = 305.6 cfm

AIRFLOW CONVERSION CHART MULTIPLIERS
If you want flow at:






If you have flow at:
3" 5" 7" 10" 12" 15" 20" 25" 28" 30" 35" 40" 45"
3" 1.00 1.29 1.53 1.82 2.00 2.24 2.58 2.89 3.05 3.16 3.42 3.65 3.87
5" .774 1.00 1.18 1.41 1.55 1.73 2.00 2.24 2.37 2.45 2.65 2.83 3.00
7" .655 .845 1.00 1.12 1.31 1.46 1.69 1.89 2.00 2.07 2.24 2.39 2.54
10" .548 .707 .837 1.00 1.09 1.22 1.41 1.58 1.67 1.73 1.87 2.00 2.12
12" .500 .645 .764 .913 1.00 1.12 1.29 1.44 1.53 1.58 1.71 1.83 1.94
15" .447 .577 .683 .816 .894 1.00 1.15 1.29 1.37 1.41 1.53 1.63 1.73
20" .387 .500 .592 .707 .774 .866 1.00 1.12 1.18 1.22 1.32 1.41 1.50
25" .346 .447 .529 .632 .683 .775 .894 1.00 1.06 1.10 1.18 1.28 1.34
28" .327 .422 .500 .598 .654 .732 .845 .945 1.00 1.04 1.12 1.20 1.27
30" .318 .408 .483 .577 .632 .707 .816 .913 .966 1.00 1.08 1.15 1.22
35" .293 .378 .447 .535 .586 .655 .756 .845 .894 .926 1.00 1.07 1.13
40" .274 .354 .418 .500 .548 .612 .707 .791 .837 .866 .935 1.00 1.08
45" .258 .333 .394 471 .516 .577 .667 745 .789 .816 .882 .943 1.00

Another helpful resource brought to you ONLY by Airflow Research and Century Performance Center, Inc.

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