We have added a K&B 3.5 only racing class in the Twin Cities. Any hull type is allowed, but it must use a K&B 3.5 engine. In my case I put my 3.5 K&B into an old JAE G2 hull. It weighs 4 lbs. and uses a 45 Zipp strut with ball bearings. So far the best prop has been a 1715-17-45. Today I tested some pipes to see which was the best with it. Speeds are peak speeds as determined with an onboard Futaba telemetry system (GPS). NovaRossi 21 pipe at 8-1/4" to the weld - 45 mph. CMB 21 pipe at 8-1/4' to the weld - 53 mph. Bouchie 21 pipe at 8-1/4" to the rearmost weld on the converging tail cone - 54 mph. Zipp Kits new 21 pipe (same dimensions as the Bouchie pipe) at 8-1/4" to the rearmost weld on the converging tail cone - 56 mph. So the winner is the new Zipp pipe. The water was choppy so I think 60 would be possible on flat water. The new Zipp pipe is really nice looking too. It is aluminum but polished to a mirror finish.