Doesn't it depend then? I always thought you did. But if you turbo a car with a high psi turbo, wouldn't you have to lower the compression. Correct me if I'm wrong but, isn't there a connection between the engine's compression and the rpm's. This is my logic, NA cars usually rev high and fast because of their high compression (and igntion system but for our sake, lets just stick to compression), whereas, turbos take longer to rev up. I always thought that turbos take long to rev up because the compression is low or it has to be lowered so the turbo can be used to its capabilities. Please, if I am wrong in anything, correct me. The last thing I would want is to mislead someone with inaccurate information.