I have 9 HB PDP motors at this time. Some are marine and some are aero. The company made a
"Blitz" version of the PDP motors also. These have chromed sleeves and timing is increased. They are quite powerful and have conventional rings. I have a few of the Blitzs and with a pipe they will hang with a non piped ABC all day long!!
All PDP motors are Dykes ringed. As has been mentioned earlier they are a 2 ball bearing motor, outstanding fit and finish and have great carbs. They start usually the first try and idle as good as any motor made bar none!!!! If you ever need rings for these motors try Frank Bowman in Farmington NM. He MAKES a hardened steel replacement ring that is far better than the one sold by MECOA. The original bearings last for ever and should be saved if possible. I have cleaned up several of them that seemed gumed up and they work great. Replacement bearings can be had at any good bearing supply house but cannot match the quality of the german originals including Boca!! One other thing I am doing with them now, is shimming the cylinders 10-15 thousands on the PDPs to increase timing and putting a pipe on them. They respond to this change very well. Remember you must also ad shimming to the head button also. They do well on 20% nitro this way too.

Finally, although they fall behind some of the newer ABC motors for power by a bit, they have GREAT torque, ie bigger prop, and will outlast the ABC motors if you compare ring vs ABC by a mile. I have one that is 25 years old and on the original ring still.

I plan to continue to build my collection of these fine motors so if anyone has a PDP out there they want to get rid of let me know.

Regards Curt Risner