650 CFM RT X Viper carburetor with mechanical secondary combines the durability of a pressure forged carburetor with the performance of billet metering blocks and bases, 4 corner idling, and a 3-port race ready viper bowl. These carburetors are ideal for the road and track vehicle, looking for the best in carburetor performance, while maintaining an affordable cost. The R-TX Viper Series carburetors come with red billet metering blocks and black billet bases, the 3-Port Viper Bowl, and 4 corner idling. They boast the latest technology in air and fuel calibrations, as well as all the performance tune-ability for your track day needs. The 3-Port Viper Bowl will not fit a drop base air filter.