The S series of alternators feature hairpin stator technology for un-matched output at idle. The 170 amp S series unit makes 140+ amps @ 800 engine RPM, and achieves full output by just 1800 engine RPM. These units are extremely durable, built with twin rectifier plates and 12 oversize diodes. The 170 amp unit makes great power all the way down to 400 engine RPM and are great for high RPM racing applications.