David,
I don't know, I ordered a 8" JP w/my boat when it came in it had a 10" on it I questioned it due to how far the pad was set up under the boat. My top end has consistently been between 70 & 71 gps. w/ 2 men and tournament load 3/4 tank of gas. Have never run it w/light load assume it would do around 75+. In the winter (cool months) I can't run WOT full trim gets into the rev limiter, have to tuck the engine just a tad. Running a 25 pitch Tempest 2 3/4" below pad. I would love to try a 26 or 27 pitch now, tried a 27 when engine was new and not real loose. slow out the hole and and was a few hundred rpms from max. but still hit 70 w/load and if I remember right 74 by myself w/all my gear. would like to try a 27 tuned/blue-printed prop. guessing it would probably be around 72-73 w/load and 78 light. as far as loosing top end I don't know, I don't know of one w/a 225 and no JP got nothing to compare with. Low to mid 70's w/load is pretty good for a almost 21' boat w/225 and 25 pitch prop. theoretical speed for a 25 pitch with my gear ratio is about 77 mph I'm running less than 10% slip w/a load and only about 4% slip light. really can't expect more than that. KENNY
