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Stock CR for a B18A1 or B18B1 is 9.2:1. A GSR is 10:1, and type R is 10.6:1.
You can run up to about 11:1 compression on 93 octane. 10.5:1 is safer if you don't want to get into serious tuning and detenation problems. With up to 9.5:1 you should be able to run regular, then from 9.5 to 10 you should run mid grade 89 octane. More than 10 and you should run super 91 or 93 octane.
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