Power plenum vs reed valve?

[mapbike]

A good pocket bike pipe is a good pipe. and getting good mid range on the track is probably what you want, what I'm talking about is a pipe that gives reasonable low to mid with a big header pipe, but starts to work around 7000. I find the standard pipe starts to become a problem here, and no doubt an open pipe has it's big advantage around now.
But a good expansion chamber with motor tuned to suit, can start to run really nice around 8000, even with a 'silencer', and give a real 'push' all the way above 9.

I agree 100%..... now if I could only find that pipe and get that set up on my bikes...... that has been my issue so far.... I can get good low to mid pull all the way to 37-38mph with all the expansion exhaust I've rigged up so far, but in order to get the top speed.

I included pix of the best overall performing exhaust I've had on my bikes, it is built from a stock header pipe and the I took a muffler that was made for the larger Briggs Lawn tractor engines 8-12HP, I cut the threaded end off and brazed the header pipe in, then I took a 5/8" drill bit and drilled through the diverter plate that is inside the muffler that directs the exhaust flow into the chamber through perforated inner tube of muffler, I went down to a local muffler shop and had him swell a piece of exhaust pipe so I could make the slash cut tip just to dress it up a little, its not quiet but it really performs better than anything else I've had on my fastest bike so far.

Map

 

[mrfubs]

I find this hard to belive, any 2 stroke iv known that is making its full potential power needs a expansion chamber or else the whole 2 stroke process does not perform correct.

 

[Theon]

A properly tuned expansion chamber is said to 'super charge' a 2 stroke at a certain spot in the rev range.
An open pipe I think can do a similar thing, but I think you will find it has to be something like 6 or 7 ft long.

 

[mapbike]

I find this hard to belive, any 2 stroke iv known that is making its full potential power needs a expansion chamber or else the whole 2 stroke process does not perform correct.

We can all believe what we want to, I personally believe what I have done and seen and experienced with my bikes and with the many different exhaust I've tried on them, I dont talk out my back side and if I tell something as a fact then you can bet your sweet backside thats the way it is in my experience, not one time have I said expansion pipes are bad are that they dont work, but I wish someone would find one that will work on my engines better than what the exhaust I built for it does, it has a small pocket bike pipe on it now and it runs good and sounds good but has a top speed of about 37.5 MPH according to GPS this same bike and same engine would run 45+ a on flat ground with the shorty pipe shown in the photo, it is a very loud pipe but out performs anything else I've had on this bike hands down.

I have the shorty pipe on a new engine I just built up yetsterday now, took it out for its maiden ride, and with only 10 miles on the new engine I GPS'd 45.8 mph on a slight decline, not sure what it will do on the flat when its broke in good but it pulls hard from 15mph all the way up to top speed with the homemade shorty pipe, I cant explain it as far as why it works so good on my egines all I know is that it does and no matter what other pipes I try, this one is always the one that performs the best all the way around on any of the four bikes I've had it on.

Several people have built very good running bikes on here without expansion pipes, mine runs good with some expansion pipe exhausts that I've tried and have good torque but don't have as good top speed as they do with the homemade shorty pipe.

below one of bairdco fast bikes

Another of bairdco fast bike, this was a race bike of his and he was running a set of super tough clutch pucks I made for him for the Death Race that year.

and another

Here is the only bike of his I ever seen with an expansion pipe.

The only point I'm making here is that these china girl engines can run very good and be very fast without running an expansion exhaust, and if the expansion pipe isn't right for the engine, it will hurt top speed performance instead of helping it, been there done that on my bikes that are capable of high RPM's and faster top speeds.