The 8.5:1 CR in the 70's was due mostly to government regulations. They removed lead from our gas and introduced strict emissions limits. In the 60's we had 12:1 CR on performance cars from the US manufacturers. I had a 62 Oldsmobile Jetfire that had an all aluminum V8, a turbo, 10.5:1 CR and an alcohol injection system. This was stock from the factory! With computers and years of engineering improvements we have seen engine performance exceed the levels previously achieved and still have cleaner air.
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