all a 383 is, is a short bore 400, I personally don't know anyone that races a short rod (5.56) 400 since there is a horrible rod ratio that robs power, everyone now days runs longer rod (5.70-6.00) 400's since pistons are widely available, yes, in my case a 383 would be better since 170cc intake ports feed 383 cubes better than 412 cubes, but if my intake ports were larger i would go with the 400. heres a good question for you guys, what would you go with if they were the exact same price-406 or 383?