Hello Paul, that compression ratio info is in fact correct BUT you also need to take into account that many turbo cars have an intercooler and most all aside from diesels have aluminum heads which pushes the FCR up a little higher. Normally on a naturally aspirated engine with cast iron heads you max out at around 10:1 with pump gas before detonation starts to occur. If you are running aluminum heads you may be able to bump that up a point to a point in a half to 11.5:1 but that's pushing it. Depending on the altitude where you live also affects the final compression ratio which you can calculate in the Corrected Compression Ratio formula below. Now with all that said running gasoline with ethanol which is about all you can buy in most places pushes the FCR limit back down again. If you can buy ethanol free 93 octane fuel (we have it here at Shell) that is the best thing to run aside from race fuel.
Below is a quick reference chart I pulled from the BDS website so you can see where your final compression ratio is at without doing all the calculations.
Final Compression Ratio Chart
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This chart shows the final compression ratio 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 "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.
Corrected Compression Ratio = FCR - [ (altitude÷1000) x 0.2 ]
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