BMW may also be cautious regarding hp claims with variance due to climate conditions...ie hot temps. When you are drawing in extra air with turbos, the extra ooomph with cool, dense air is very noticeable. Flogging your car at 60 F vs 95 F feels very different on the butt dyno. There is likely a standard utilized in the industry that I am ignorant too, but forced induction likely creates a broader range.
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-kskpsu
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