Edelbrock's Annular Flow Booster technology brings superior fuel atomization to all dual-quad applications with the AVS2 500 CFM Carburetor #1903 that is specially calibrated for engines running two four-barrels. Annular Flow Boosters deliver near EFI-like drivability that you can feel as soon as you step on the gas. Fuel distribution is refined by eight equally spaced orifices in the booster rings that replace down-leg boosters which simply dump raw fuel into the venturi. Flat spots are completely eliminated, and throttle response in the low- to mid-RPM range is improved tremendously with no sacrificing of that top-end power that Edelbrock is known for. The AVS2 is unaffected by engine backfires since there are no power valves to blow out. For fast and simple part-throttle tuning, metering rods and springs can be changed in seconds without carburetor removal or fuel draining. AVS2 carbs have the unique ability to "hold a tune" when compared to other carburetors. Your tuning and adjustments stay unchanged, so performance remains consistent. Updated primary and secondary booster clusters in the AVS2 offer the most accurate and up-to-date calibration available for today's fuels and octane levels. Additionally, the unique Qwik-Tune Secondary Air Valve allows for limitless calibration of the secondary circuit. Adjustments can be with simple hand tools in seconds to suit your application. The AVS2 features a two-piece ease-of-tuning design that lets you make float level adjustments or replace internal components without draining the fuel from the carburetor or removing it from the engine. The AVS2 500 CFM carburetor is available with electric (#1903) or manual (#1904) choke in satin or EnduraShine finish. For small-cubic-inch single carburetor engines, order the specially calibrated AVS2 500 CFM #1901 (electric choke) or #1902 (manual choke). Like all Edelbrock carburetors, the AVS2 Series is designed, manufactured, assembled and calibrated by Edelbrock in the USA.