They recommend a 45 because you can always choke it down, but with a 40 you reach a limit with larger venturis. My motor is mostly stock. Flat tops, 292 cam, shorty header, Ansa exhaust and a 123 Ignition. I am going to take the leap to dual DCOE this winter though. Mostly for the challenge. Lol. Jason Sent from my iPhone using Tapatalk