I just completed installing John's S-C and C-G and tuning the smoke unit on my JLC Challenger 6-28099. (By the way John, thanks again for your help with the install). Here are some of the things I did and the results thereof.
The intake hole was enlarged to 7/32nd" (above the fan). I went with this size to match the approximate diameter of the inner fan blades opening. Any larger and I thought the inlet hole would start to expose the fan blades resulting in a less efficient air flow.
The exhaust was enlarge to 5/32nd". The exhaust hole enlarged is in the casting that attaches to the top of the smoke unit. I wanted to reduce the discharge restriction without causing the casting to come loose. However, as this casting is held in place with screws, I probably could have made this larger. I also replaced the batting and tested the resistor, which was original and still tested and looked good. I also oiled the fan motor upper sleeve bearing.
The attached photo shows the holes enlarged. Notice the shinny interior of the exhaust stack showing the metal removal. I wish I had recorded the original diameter of the holes. I could have then calculated the % increase.
What I found is the smoke output was greatly increased. So much so i now have to turn the smoke unit off to clear the room of smoke after only several minutes of run time. I also noticed the exit velocity of the smoke has increased. On this particular engine there is a wedge divider/diverter right above the smoke unit's discharge. This splits the smoke flow into the two exhaust stacks. When in idle, the smoke flow seems to be fairly even, with maybe the back stack with a little more flow. But, to me, very acceptable. With the engine running (chuffing), the amount of smoke from each stack, again seems to be the same. I will note, that the increased air velocity going through the lower internal diverter, pushes the smoke forward and back. In other words, the smoke does not go straight up. Here again, there seems to be the same amount from each stack.
Let me know if this is of help to anyone.
