RE: tune pipe for a .15 CV-A
The CVA .15 is a pipe timed [185 degree] MO-FO! It really likes MAS 7x5s and 7x6s! [skinny blade series].
MACS model airplane exhaust products has everything you need, just GOOGLE search it.
APCs' web site also has stuff to look over. They used to make a 6.5x6.5 prop that really worked well, but last time I looked, wasn't there. They have a very good selection of props over there at any rate.