Lowering the compression ratio will let you boost more since you have less chance of pre-ignition, but you sacrifice HP\TQ on the lower end (more noticeable turbo lag). So lowering it a lot will give you great room for boost, but you would be crawling off the line. On the opposite side, the people who want to go N\A would increase their compression ratio, sometimes to 11 or 12 to 1.
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