The standard 91.5-00 OEM oil pump comes in a thickness of .373. The VVT high-volume OEM pump comes in a .393 thickness. Boundary Stage 1 pumps are .373 with billet gears to increase flow, and the Stage 2 pumps are machined to .430. Along with the many other improvements they make to the gerotor pattern, the Stage 2 pump provides an easy 10% flow over the OEM VVT spec high-flow pump, or 15% more over the 91.5-00 NON-VVT OEM pump. That extra flow gives you more idle to mid-range oil pressure as well as reaching maximum relief valve pressure faster. The relief valve shimming only affects your max oil pressure (5000 RPM plus). These pumps have tested privately up to 100PSI with no ill effects, but testing has shown 76 PSI being most beneficial to bearing and tappet wear without cold start pressures being very high. More oil pressure equals longer engine life!
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