at moment I have a 11x8 on my Rossi 65 2 stroke... I have tuned it to round 12800 on the ground... I would expect it to hit round 14K at least in air... the plane is traveling pretty fast but I would like to try gain a little extra if possible... at the hobby shop there is a 11x9 sport and then 11x10 patern prop... now if I use the 11x10 patern, what would it equate to in a 12inch diameter prop? 12x8? or is patern different?... I guess actual question is would I gain more speed with the patern prop or not? and how many revs should I expect to lose with the 11x9 and also 11x10?

Do the math yourself. With a pitch of 10 inches, turnng 10,000 rpm, that prop travels 10,000X10 inches per minute or 100,000 inches per minute. That's 8300 feet per minute or 500000 feet per hour or 94 miles per hour. This is ideal, with no drag and no slip of the prop.

CGr.

Hi!
You would not probably gain more speed!!!
Old style 11x7, 11x7,5 and 11x8 " props suits "old style" (fast flying) pattern planes like the Hanno Prettner "Curare" and such.
For more modern (larger, with lighter wing loading) pattern planes that flies slower, larger APC props work best.
Soo ...What plane do you have???
Remember also that if you put on a larger prop you have to lengthen the pipe (trail and error process).

its in a 46size GP Revolver... not a patern plane... so I wont go with the patern prop then... I would try the 11x9 and also maybe a 11x7 then... easiest way to find out ima put a gps on it next weekend...