Machined from red anodized billet 6061 aluminum with square surfaces, excellent umbrella valve sealing, longer main breather exit nipples with dual O-rings to promote better breather system sealing. Properly sized breather inlets and location for optimum engine breathing. Unique design maximizes breather volume and allows for easy serviceability. Breather bodies have multiple drain ports located on the inside floor, ports are chamfered on ID to allow easy drainage yet squared off on exits to deter filling from splash oil. Kits include: billet breather housings, billet covers, breather filter elements, umbrella valves and quality hardware. Feuling cylinder head breathers work, seal and you will find they hold an engine vacuum. Testing shown on a healthy engine will see 3-4 oz of oil in the sump and once the dipstick is removed another 3-4 oz will drain. Note: Factory plastic OEM breathers can be problematic, material easily distorts, especially after seeing excessive heat then the internal umbrella valve struggles to seal, causing oil carry over. Another issue found with the OEM breathers is cracked and or broken exit nipples which can be caused by heat distortion and or improper fit and poor installation. This can cause the oil filled air to bypass the stock breather entirely. Note: Feuling breathers work, seal and you will find they hold an engine vacuum. Testing shown on a healthy engine will see 3-4 oz of oil in the sump and once the dipstick is removed another 3-4 oz will drain. Note that this test procedure can only be performed with a sealed engine meaning no external venting via dipstick or trans top cover. Breathers can be used with external venting via dipstick, trans cover and air cleaner. Note: See 707761 for Feuling rocker cover rebuild kit that fits OEM and Feuling billet aftermarket breathers.