This 320 amp S Series small case alternator is all about max power and is not designed to charge at low idle speeds. Vehicles with small crankshaft pulleys and idle speeds below 800 may not charge at low idle. If power at lower idle speeds is what you need please look at our 240 amp S Series alternator. This S series 320 amp 6 phase alternator offers incredible output in a compact and durable package. 12 diodes, twin rectifier plates and outstanding airflow ensure long service life, even in severe conditions. 320 Amps of power at cruising speeds and 140 amp of power at 800 RPM (assuming a 3 to 1 crankshaft to alternator pulley ratio). This alternator comes with a 1.75" diameter pulley and may require being installed with a belt slightly shorter than stock.