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This controller allows normal timing settings for easy starting and reasonable fuel economy under regular driving situations. As the engine goes into boost, this timing setting may cause detonation. So this boost retard controller allows the driver to dial in ignition retard with a dash-mounted knob. This device (Holley PN 91070) operates on a degrees of retard per pound of boost and is typically adjustable from 1 to 3 degrees of retard per pound of boost.