Staff Answer
May 05, 2026 - 10:34 AM
Its usually only the alternator pulley where there is any kind of option to choose the diameter. It’s all about the "Speed Ratio" betwen the engine and the alternator. Typically the alternator will spin two or more times as fast as the engine. To find the exact alternator RPM for any given engine RPM, use the formula in this article.
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Goal: You want the alternator to spin between 4,000–5,000 RPM at your cruising speed.
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Caution: If you choose a pulley that is too small you will have less area to come in contact with the belt and you risk over-spinning the alternator at Wide Open Throttle
