gored expanding elbow versus stamped elbow

[berkshire]

A quick question. I am a little out of my depth here.
I am prototyping an engine installation for a 2 cylinder 2 stroke. In order to get the package to fit I have had to put a 180 degree bend in the expansion cone just before it goes into the muffler. According to what I know, this bend should be smooth i.e. stamped elbow. For expediency and to see if everything would fit, I just took a band saw to the expansion cone and made a 12 gore welded tapered elbow, fully intending to replace this with a stamped elbow. Now I have a business associate saying that as long as the gores are round, the sonic wave will reflect back around this elbow just fine and that we can run the engine just fine with what I have. I am a little suspicious of this. What is the groups opinion?

 

[dgallup]

I have seen race bikes with pieced together expansion chambers like what you are describing (I think). They appear to work well. I'm sure it all depends on how well you laid everything out and the quality of the welds on the inside.

 

[berkshire]

Well thats one for.
I ground the welds inside before making the last joint.
The guy who suggested this is a dirt biker.
B.E.

 

[Tmoose]

IN the late 60s Gordon Jennings thought angles in the diverging and maybe converging cones weren't too big a deal.
page 61

http://www.vintagesleds.com/library/manuals/misc/Two-stroke Tuner's Handbook.pdf

An "expansion cone" without a converging or baffle cone would seem to be missing the plugging pulse and risks losing fresh charge out the exhaust.

 

[berkshire]

Hi T moose,
I looked through your book by Gordon Jennings, I actually had the relevant pages on expansion chambers, but I did not know where they had come from. So what I am getting there is the same thing my business associate is saying," the place for smoothness is in the narrow pipe before the cone.The larger sections can tolerate discontinuities as long as they are round in section and not oval or flattened." My fear was that the reflected wave would be diffused by the gores of the big elbow.
This particular exhaust has the baffle cone buried in the muffler so it does get a stuffing pulse.
B.E.