My 572" made 1231 hp.@ 8400 and 865 tq@ 6800 on a tight dyno....my new 604" won't be going on a dyno , but it should make north of 1260hp.... Steve gill has a 556" that made over 1240 from what I heard... As far as results... Well ,I've been over 160 mph. In my boat with the 572"..