thanks a lot for the information, just a shame that I never found this before - I see the post has been there for more than a year!
Juris Ramba has given me a similar description, but unfortunately also a day after I made my silencer...
Well mine is empty at the time being, the idea was to add something to the rear end of the inlet pipe and/or insert a baffle tube into the outlet tube, depending on how much noise the thing makes! As you wrote on 25.7.2009, I can still weld an extension with slots to the exhaust pipe. I understand this was originally a part of the silencer canister, but making it as a part of the pipe has the advantage that you can get at it to modify the slots or just to clean them!