The Tomei Oil Gallery Orifice controls the amount of engine oil that is delivered to lubricate the parts in a cylinder head. The stock oil-gallery orifice has been designed for general street and daily driving use so the hole is too large and it allows too much oil to be delivered to the cylinder head which will cause the list of possible problems as noted below.
(1) Too much blow-by Gas,
(2) Blowing engine oil,
(3) Leaking oil from valve guide,
(4) Insufficient oil delivery to the crank journal,
(5) Miss-breathing air from oil pan under the horizontal G Forces
The design of the TOMEI oil gallery orifice is based on the experience of developing N1 endurance and drag racing engine. By limiting the diameter of the orifice to φ1.5mm (φ2.0 Standard), Tomei succeeded in securing enough lubrication to the camshaft and valves while gaining amount of oil in the oil pan, and suppressing these problems. (To prevent blow by, Tomei recommends using the TOMEI 3D profile pistons.)