First off yes the cam is actually ground advanced to make up for late model stock timing chains being made with retard in them. Secondly When you retard a cam you bleed off cyl pressure because the intake valve is open longer when the piston comes back up on the compression stroke thus but it improves cyinder scavenging at higher RPM...So that brings us to advancing the cam. Advancing builds more cylinder pressure at the expense of cylinder scavenging at high RPM...The more cylinder pressure you build the more/flatter you torque curve will be.
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