I have a funtanax with a evolution gx26 in it

what would be a good 3d prop for this plane/engine combo?

i have a 17x8 on it now and it bairly pulls 7500 rpm on the ground

are you sure the high end is tuned ,,that seems anemic for a 26.... try a 17x6 if you cant get anymore rpm out of it my 20 hits8400 on the ground with a xoar 17x6

thats what i thought, maybe it needs to break in a little more?

I put a tuned pipe on it and now get a little over9000rpm out of a 18x6 on the ground

what a difference a pipe makes!!!!!!