The Holley model 4150 (#0-805310) was originally used on the 502/502 big-block engine. This carburetor is an excellent choice for all 502 crate engines. The vacuum secondaries and electric choke make it ideal for street, strip, towing, and off-road vehicles. Technical Notes: It has vacuum secondary, automatic electric choke, dual feed, and center hung fuel bowls. This part number contains the carburetor, gasket, mounting studs and nuts. Replacement components are available at any Holley carburetor retailer.