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Compression Ratio

This chart shows the final compression ratio by combining the static compression ratio of an engine and the maximum blower boost from the blower system. It is to be used as a guideline in determining the proper maximum boost level for a specific application. Final compression ratios in excess of 12.4:1 are not recommended for use with "92 octane pump gas". The higher the final compression ratio, the higher the octane rating of the fuel must be in order to help prevent detonation and serious engine damage.

The formula for calculating your exact Final Compression Ratio is as follows:

Final Compression Ratio (FCR) = [(Boost/ 14.7) +1] x CR

COMP RATIO

2psi

4

6

8

10

12

14

16

18

20

22

24

6.5cr

7.4

8.3

9.2

10

10.9

11.8

12.7

13.6

14.5

15.3

16.2

17

7

8

8.9

9.9

10.8

11.8

12.7

13.6

14.5

15.3

16.2

17

17.9

7.5

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

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

9.7

10.8

12

13.1

14.3

15.4

16.6

17.8

18.9

19.8

20.9

21.9

9

10.2

11.4

12.7

13.9

15.1

16.3

17.6

18.8

20

21.2

22.4

23.6

9.5

10.8

12.1

13.4

14.7

16

17.3

18.6

19.8

21.1

22.4

23.6

24.8

10

11.4

12.7

14.1

15.4

16.8

18.2

19.6

20.9

22.2

23.6

24.8

26

10.5

11.9

13.4

14.8

16.2

17.6

19.1

20.6

21.9

23.4

24.8

26.2

27.6

11

12.5

14

15.5

17

18.5

20

21.6

22.9

24.5

26

27.5

28.9

 

Boost = Maximum blower boost

14.7 = PSI at sea level       CR = Engine Compression Ratio

Altitude plays an important role in determining compression ratios. If the altitude in the area where you normally drive is significantly higher than sea level, then your compression ratios will also vary. To determine the effects of the altitude on a calculated compression ratio, use the following formula:

Corrected Compression Ratio = FRC – [(altitude/1000)x 0.2]

 

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