I went through this on my DA-50. I'm running a KS86 (I believe) canister and the standard exhaust header. My problem involves a power band issue where it will jump from about 4,500 to 5,500 rather abruptly. After talking with DA, TBM, and making posts here and other places, here's what I've learned:

1. The shorter the header, the narrower the band (bigger spike in power) for a given size prop.
2. A bigger prop needs a longer pipe. A smaller prop can use a shorter pipe.
3. The stock DA pipe is 10.25" as measured along the curves on the centerline. This is the only header DA offers (from what I understand).
4. I am using a 23 x 8 prop. Using a 22 x 8 may solve my power band problem.
5. You shouldn't use the silicon union to extend the length of the header. It will burn through. If you want to lengthen the header, get a small section of pipe and two silicon unions.
6. My problem may be a rich low end. My cylinder head temp as measured after a flight while idling is 145*F MAX! I need to go leaner on the low end needle most likely. I should be hitting 180* or 190*.
6. The big caveat for me in all this is that adjustments on a fresh motor are tenuous. I only have 4 gallons through my DA. It's probably not ready for fine tuning. When I lean out the needles, my power band problem might go away.

I fly a 50cc Aeroworks 260 weighing in over 16 pounds. Vertical is no problem. The only 3D problem is that spike in the power band. I'm using a 23 x 8 Zoar prop.