The Edelbrock 18049 Remanufactured Thunder Series AVS 500 CFM manual choke carburetor has been designed and calibrated to deliver optimum street performance in Dual-Quad applications. Several characteristics make the 18049 Remanufactured Thunder Series AVS 500 CFM manual choke carburetor an outstanding street performer. The first one is that metering rods are utilized to transition between circuits. The carburetor is unaffected by engine backfires, which means that there are no power valves to blow out, and the rods can be changed in seconds without carburetor removal or fuel draining. Secondly, the carburetor has the unique ability to "hold a tune", so once it is tuned, the carburetor stay’s tuned. What this means to you is that compared to other carburetors, the performance remains consistent and the calibration stays unchanged. The third characteristic is the primary and secondary booster clusters that are utilized offer the most accurate and up-to-date calibration available for today's fuels and octane levels. Fourth the unique Thunder Series' Qwik-Tune Secondary Air Valve allows for limitless calibration of the secondary circuit with simple hand tools while on your vehicle. It's quick. It's simple. It's effective. It can be easily adjusted - in seconds - to suit your application... no extra parts required to achieve optimum performance. Simply put the Edelbrock 18049 Remanufactured Thunder Series AVS 500 CFM manual choke carburetor is undeniably the most innovative and dependable street performance carburetor available today.