I had a performer on my 455 with a 600 carter in my 18ft jet boat. when the motor blew I put it back together bored .30 over and bought a tunnel with a single 800 holly, second time around it ran -5mph when I thought it would do +5. I am not a "gearhead" by any means, my uncle who is, went out with me yesterday to make sure timing, vacuum leaks, and general assembly was o.k. in about 10 minutes he got me an additional 4 mph which brings me up to 56, when my old motor hit 61. same hull, same pump, pretty much same weight. what do you guys think. is it the intake? oh, yeah same heads too.