FINAL COMPRESSION RATIO CHART WHEN USING A SUPERCHARGER

This chart shows the final compression ratio in your engine by combining the static compression ratio read down the left side and the amount of boost applied to the engine across the top. Use this chart shown below as a guideline to determine the proper amount of maximum boost level for a specific application.

Final compression ratios above 12.4 to 1 are not recommended for use with "premium pump gasoline." The higher the final compression ratio the higher the octane rating of the gasoline must be in order to help prevent detonation and serious engine damage. Final Compression Ratio (FCR) = (Boost / 14.7) + 1) x CR Boost = Maximum Boost 14.7 = Psi. at Sea Level CR = Engine Static Compression Ratio
Altitude plays an important role in determining compression ratios. If the altitude in the area where the vehicle is driven is significantly higher than sea level then the compression ratios will vary. To determine the effects of the altitude on a calculated compression ratio use the following formula:

Correct Compression Ratio = FCR minus [(altitude/1000) x 0.2]


Compression                  Boost (in pounds per square inch)
Ratio



         2    4    6     8    10    12    14    16    18    20    22   25


6.5:1   7.4  8.3  9.2  10.0  10.9  11.8  12.7  13.6  14.5  15.3 16.21 17.0
7.0:1   8.0  8.9  9.9  10.8  11.8  12.7  13.6  14.5  15.3  16.2 17.0  17.9
7.5:1   8.5  9.5 10.6  11.6  12.6  13.6  14.6  15.7  16.7  17.8 18.6  19.5
8.0:1   9.1 10.2 11.3  12.4  13.4  14.5  15.6  16.7  17.8  18.9 19.8  20.9
8.5:1   9.7 10.8 12.0  13.1  14.3  15.4  16.6  17.8  18.9  19.8 20.9  21.9
9.0:1  10.2 11.4 12.7  13.9  15.1  16.3  17.6  18.8  20.0  21.2 22.4  23.6
9.5:1  10.8 12.1 13.4  14.7  16.0  17.3  18.5  19.8  21.1  22.4 23.6  24.8
10.0:1 11.4 12.7 14.1  15.4  16.8  18.2  19.5  20.9  22.2  23.6 24.8  26.0
10.5:1 11.9 13.4 14.8  16.2  17.6  19.1  20.5  21.9  23.4  24.8 26.2  27.6
11.0:1 12.5 14.0 15.5  17.0  18.5  20.0  21.5  22.9  24.5  26.0 27.5  28.9

The above information was supplied by Blower Drive Service,"BDS."

Blower Drive Service

Return to articles