I've talked to several older mopar guys that have told me a good tuned 440 will out do a 426. I've run several 440 an 383's no complaints here. I got fresh 440-6pk on the stand for my '71 challenger, I can't wait to get it in an fire it up. My dad, an old mopar man, says the 6pk with over 1300 cfm's will give me a kick thats hard to hold.