This grid is a general idea of compression ratio VS boost. It doesnt go up to 12.5, but it goes to 12 and its for getting an idea of some numbers only.
Final Compression Ratio Chart
This chart shows the final compression ratio combining the static compressionratio 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 compressionratios in excess of 12.4:1 are not recommended for use with "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
Boost = Maximum blower boost 14.7 = psi at sealevel 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 sealevel, 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 = FCR - [ (altitude÷1000) x 0.2 ] =Pump Gas = Good Gas