These carburetors that are intended for use with superchargers, and have a unique capability that allows their power valves to reference the intake manifold vacuum below the supercharger. This allows the power valve to operate as it should, based off intake manifold vacuum. A power valve provides further enrichment to the main metering system under load (low vacuum) conditions. Without this external referencing, the power valve would be "reading" the supercharger vacuum, which has no bearing on the engine load.

Features

Tumble polished shiny finish for good looks

Small block Chevrolet 1x4, 170 series blower calibration

Manual (Cable driven, hand operated) choke for precise cold start control

Dual accelerator pumps for addition fuel under initial acceleration

Dual feed fuel inlets for constant high volume fuel delivery

Mechanical Secondaries for perfect off the line launches

4 corner idle allows you to precisely control your idle system

Intended for lightweight vehicles w/ manual trans or automatics with high stall & low gearing

Boost referenced power valve for proper enrichment under acceleration

100% wet-flow tested by Holley technicians to assure it arrives ready to run!