Hi:
I used an 11-3 wooden prop on my BG HP .40 piston and cylinder. Remember to run it fast and wet. Do not run it cold. Did you receive Instructions with your p&c?
Mr. Gardner made it very clear to me, do not use any castor oil in his p&c! He suggested 20% synthetic and no nitro! Thus far, my engine has run perfectly and still makes a very loud noise when passing over tdc.
For information, e mail Mr. Gardner as he give you the straight scoop re his products. He is a good person.
Good luck,
Frank McCune