Questions about two stroke expansion chambers.

[LonesomeTriZ]

Well this is embarrassing. Here is the story:

I was showing off some trike photographs to one of the guys I work with over here and I sounded very intelligent when speaking of their mods and how to ride them. I even got him wanting to get into trikes when he gets home. Until he asked me about the expansion chamber. He asked, “Why does the exhaust pipe expand out then get skinny again?” And I responded with “oh that is because…Um… It… Well it has to… Well, damn.” I could not believe I did not know the answer to that. So, why does two stroke exhaust pipes expand out then get skinny again? And why do some of the smaller CC two strokes not have this feature? I plan to design a custom exhaust system for one of my Z’s and this information would really be helpful.

[factoryX]

hope this helps...

http://en.wikipedia.org/wiki/2_stroke

[LonesomeTriZ]

Damn, that is cool. Thanks for sharing. That helps with the 250 CC and up. But why does my 125 and 175 not have an expansion chamber similar to the larger CC engines?

[factoryX]

different setup. it may not be as big asthe 250cc pipes but they do the same thing.

[LonesomeTriZ]

I see. This is a subject I never thought about. it is about time I learned something about it.

[LonesomeTriZ]

Here is some more good information.

http://en.wikipedia.org/wiki/Expansion_chamber

I usually stay away from Wikipedia, but lately the gear head stuff has been helpful.

[NOS_350X]

Damn, that is cool. Thanks for sharing. That helps with the 250 CC and up. But why does my 125 and 175 not have an expansion chamber similar to the larger CC engines?


Most the older/smaller bikes dont or didnt have the technology about the exhaust they have now.

[tri-Z ripper]

Good Info Nice Find!!

[Billy Golightly]

True expansion chambers are expensive to make even for the manufacturers. The smaller bikes normally are not justified to build them. Often times they'll instead use a funky design like what is common the Zinger and the smaller YTs, like your use to seeing because it does sort of work, and their cheap to make, easy to fit. Its not that they arent capable of using one, but they just normally dont because of the costs involved. A lot of the higher end mini dirtbikes in the 50cc range use them. Heres a pic of a Cobra brand bike which is actually like THE bike to have if your racing in a 50cc class now a days. Not even the KTMs can hold a candle to them.

http://www.dirtbikekids.com/images/forsale_dhushon2.gif

[LonesomeTriZ]

That's cool. I was hoping to get some more ass out of a 175 project I am planning. I wonder if I biult an expansion chamber similar to one of my Z's it that would open it up a little.

[Billy Golightly]

Oh yeah, definitely. I have a program to do pipe designs, including laying out the cone sections on flat material where they can be printed out and traced onto metal and then rolled out. I just need a roller now I could make some of my own expansion chambers.

[LonesomeTriZ]

Did I ever tell you what a great guy you are?

[Rex Karz]

Most of the 50cc poppers are made for little kids where you don't want the powerband exploding when it comes on. For little kids you want a smooth and predictable power delivery.

[LonesomeTriZ]

I see what you are saying. But you never met my son.