HMMM my kinyon style air hammer had a 1.5 bore cylinder 10" stroke and the ports on valve and cylinder were 1/4" and I was getting 180 BPM I have since changed to a 2" bore 15" stroke ports on valve and cylinder are now 3/8" I do not use the full stroke of the 2x15 cylinder but I now get 240 BPM thats 60 BPM faster than it was before -- Bob HotAnvil Forge http://members.tripod.com/hotanvil_forge