I was wondering if anyone could tell me how a two-stroke pipe works? Why are they the so oddly shaped? Just from looking at a stock 400 scrambler pipe, there is a constant diameter section, then an expansion area, then it necks down again and finally into the muffler. How does one determine the shape/lenght/diameter of the expansion area. From what I can figure out, the exhaust gases leave the engine in pressure waves. From there, the gases enter the constant diameter section, so no changes in velocity or pressure. Next comes the "magical" expansion area. Larger diameter, increase pressure, lower velocity. Do the pressure waves build on each other in here? Perhaps giving back pressure for torque? When the gases finally go toward the muffler, are they increasing in speed? How does any of this help?

Thanks for any input,

Greg

 

In a nutshell, the back pressure keeps the fresh intake charge from following the exhaust out the pipe while the exhaust port is still partly uncovered. Since intake and exhaust occur on the same stroke, it is desirable to get as much of the exhaust out while keeping as much of the intake as possible in the combustion chamber. I'm no expert on this, and someone will surely come along with a more detailed explanation.

 

Thanks for the input. I've got the exact same machine as you do.

 

Here is some interesting info 2-stroke

 

hit here for good info and pull the page down too see!!!

 

Hit for just 2 stroke engine animation

 

Those links were excellent. Thanks guys.

 

Very nice link. Makes me wonder how that "twisty turny" HPD race pipe makes so much power? Also makes me think a lot more about an out frame drag pipe. ????

 

Whitedog,

Go for it!!!

I keep everything stock anymore but back when I was younger every two stroke I purchased had to have a new expansion chamber included in the set up. My fav was for the Kawasaki 3 cylinder, they were big, black and fat with long stingers and gosh they would sing or should I say make that bike scream.

 

i known that a longer header will lead to more torque,sharp shorter
intake exhaust will rev faster,like the hpd race pipe,velocity is dominant all the way through a large combustion chamber and the overall lentgh is short to keep high rev.
the stock pipe is basically a torquer one and low rev cauze of the long shape of the exhaust chamber and no good velocity.