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These CravenSpeed pulleys are stock diameter (OEM sized) crank pulleys, utilizing the original belt layout. Since the crank pulley diameter is unchanged, they maintain alternator output at exactly stock output levels so you need not worry about flat batteries or weak charging capabilities. Through extensive weight savings afforded by 6061 aircraft aluminum construction, power gains of up to 10% are available depending on how your MINI is set up. CravenSpeed crank pulleys come fully balanced and counter-weighted, and feature anodizing for superb wear resistance & strength.
The rule of thumb is that each pound of weight taken off the engine's rotating assembly is worth approximately 2.7HP. The concept is that the crank is a parasite; it does not put power to the drivetrain but still requires the energy produced by the engine to rotate. When you reduce this parasitic weight, you release power that was previously used only for spinning the supercharger and alternator.
Is this crank pulley safe? The pulleys on the R53's 1.6 and most new smaller engines have an elastomer (rubber ring) incorporated into the pulley that looks similar to a harmonic damper. The elastomer in the OEM pulley serves as an isolator, which is there to suppress natural vibration and noise from the engine itself, the A/C compressor, P/S pump, and alternator. The purpose of a traditional harmonic damper is to protect against crank failure from torsional movement. This is not necessary in the MINI or most modern engines because of the many advances in engine design and materials. Factors such as stroke, displacement, inline, V configurations, power output, etc., do determine when and how these harmonics and torsional movements occur.