For head vented models. Similar in function to the S&S Reed valve for Twin Cam models. Unlike the regular rotating breather valve which is opened and closed by crankshaft rotation and pre-set timing; the Reed valve uses actual pressure to open and close on the right moment; at different RPM''s this ideal moment varies. This means an advantage for the Reed valve over the regular mechanical timed breather valve in reducing oil carry over; especially in high RPM conditions. Note: Not suitable for use with crankcase vented models.