Every engine that I have built for circle track that is for a I.M.C.A. modified or U.S.M.T.S. engine has at least a 6 inch rod in it.The Dart block which is 400+ cubes will use a 6.125 rod.The benifits of using a long rod have been proven to us on the dyno and also ring wear,cylinder wear,and piston skirt wear has been greatly reduced.