Hey, im doing a canister muffler for a stihl 25cc engine. so far i have read that i need a canister 10 times the volume as the cylinder. Now, the tricky part is the header pipe. ive got one bent up, but im worried that it might not be large enough. The one i made is 5/8ths ID. it looks to be about the same size as the exhaust port, but im afraid that it will be too much backpressure with the curve in the pipe. I will try and get a pic, but i need to find my camera.
Do you guys think this will work?

A pipe with 50% - 60% of the diameter of the cylinder bore will work in all cases.

thanks.  I just kinda went on the exhaust port, and also on rcshowcase the 40cc uses 3/4"  so i figured the next size down would work.  Unfortunately i dont have calipers, or the desire to tear down my engine right now, but i think most bores are about 1-1/4 to 1-1/2 so 5/8ths puts me at about 40% for 1.5 and right on par for 1-1/4.  So it should be alright.  The header tube isnt that long (maybe 4.5" ) so it should be alright.</p>

Another thing,  with canisters, can they be 'tuned' by adjusting the exit pipe diameter and length?  This is my first go at this, so i would like to get it right.  I just love the sound (or lack of) with a canister.  plus they are a nice clean install with no need to hack up a cowl.</p>

Thanks again,</p>

                         andrew</p>

some canisters need to be tuned, so start with at least 10" pipe length.</p>

If you do not have the room to spare, use a canister that needs only short headers. (MVVS, JMB, and maybe others)</p>

i was making my own canister out of an old spray paint can.  The dimesions are actually really close to the general rule of 10 times the displacement of the engine.  With the short pipe, will it hurt performance? or will it be louder?  If I can maintain 8000rpm on an 18-6 prop it will be good for what i need.  I would go and buy one, but im trying to keep the costs down.  a new canister/header, will cost around $200.  Thats $200 i dont really have right now.

too many variables in a simple mousse can. Tune it properly like any tuned pipe.