The S series of 6 phase alternators offers incredible low RPM output in a compact and durable package. Highly efficient, these units use less horsepower than conventional 3 phase alternators. 12 diodes, twin rectifier plates and outstanding airflow ensure long service life, even in severe conditions. This unit is specially designed to replace 10DN/10SI/12SI alternators with 6.61 inch center-to-center distance bolt patterns, as used by several aftermarket accessory drive manufacturers and most 1963-1985 GM vehicles. This unit includes a specially machined March performance 6 groove serpentine pulley, fan, and decorative cover already custom fitted to the alternator, and features a simple one-wire hookup. The 1.75 inch diameter pulley on this unit will yield 140+ amps at 800 engine RPM idle speed with a 5 inch crankshaft pulley. Be sure to calculate your pulley ratio for high RPM or racing applications to ensure the alternator is not over-spun when at high engine RPM.