These Holley aluminum Ultra HP carburetors feature all-new construction for maximum performance, right out of the box. They start off with a 6061-T6 billet aluminum black, bright-dipped anodized base plate. They feature elongated mounting holes, allowing for fitment in intake manifolds with a square 4150 or large Dominator-style flange. The base plates feature a dedicated, race-only throttle lever with all unnecessary street attachment points and tangs removed. A stainless steel adjustable secondary link offers you a choice of 1:1 or progressive secondary throttle actuation for ultimate control of the secondary opening rate. They also use knurled (hand-adjustable) primary and secondary curb idle screws, a capped primary throttle shaft, factory-machined mounting holes, and a throttle body and new secondary pump cam lever designed to provide positive throttle stop on the secondary side. On top of that, Holley uses an updated main body design with air bleeds moved outward to allow for a smoother transition of airflow from the top of the carburetors into the venturi. The integrated bypass valve eliminates the need for holes in the throttle plates, helping to maintain the correct plate to transfer slot relationship, as well as good idle control when using radical camshaft profiles. Also installed is a new contoured hex head squirter for streamlined airflow, and all unnecessary mounting bosses have been removed for a smoother, cleaner appearance. Next, they add 6061-T6 billet aluminum metering blocks with improved durability, true gasket sealing, and bright-dipped anodizing for corrosion protection. The blocks are fully adjustable (emulsion bleeds, power valve channel restrictors, and idle feed restrictors). Excess material has been removed for improved fuel capacity, an integrated pry point assists in disassembly from the fuel bowl and main body to prevent damage to the gaskets, and a new snap-in-place bowl vent whistle makes removal and/or replacement easier. Finally, they finish everything off with a totally new fuel bowl design. They have 20 percent more fuel capacity than traditional V-bowls, eliminating fuel starvation, while providing more consistent air/fuel ratios. The bowls have internal baffling to help control fuel slosh and minimize float level fluctuations in hard launching or cornering situations, and a fuel shelf built-in below the needle and seat to greatly minimize fuel aeration and promote better metering. Their unique fuel trough is designed into the floor bowl to route fuel flow directly to the jets and assist in keeping the jets covered by fuel. The specially made clear Pyrex sight windows are located on both sides of the fuel bowl, making fuel level adjustments safe and easy. The new bowl also uses a better positioned built-in drain plug to drain the fuel out of the bowl, and the contoured entry point provides smooth fuel flow directly to the needle and seat. These pieces combined make the Holley aluminum Ultra HP carburetors the perfect choice for your race-only application.