Our L78 is just a stock build, 11-1 advertised compression. It seems to run just fine on 91-93 octane gas. We've put over 30K miles on it in the 10 1/2 years that we have owned the car. Now, if the engine has been machined for a true 11-1, you may just have problems with pump gas. Factory engines have been known to check out at 10-1 and even less.
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