The rule of thumb is to not have under 15 inches of vacuum at idle unless you have a bigger cam or the elevation where you live is higher. 12 inches sounds pretty good though. The best way to check it is to watch the vacuum as you are driving and have a load on the engine. It should drop to around 3 or 4.
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82- 347, SVO A4, Scat Billet Crank, Crower Rods, Nowak Pistons, TFS Heads W/Crower Stainless Rockers, Victor Intake, Gold Claw, Paxton Fuel system, MSD ignition,
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