If you've got a bit of money to spare then look for a kawasaki kx65 expansion chamber (all 2 stroke performance exhausts are expansion chambers) your "80cc" is actually 67cc so that exhaust wouuld be tuned more to the engine. Expansion chambers are tuned to the engine size, they are made in three sections. The divergent section is the first bit after the header pipe, this is an opening cone, here the gases are sped up, then they go into the middle section, here the gases expand. Next they will enter the convergent section, this is a cone (big to small) where they will bounce back causing backpressure which will keep the fuel in the cylinder, stopping it from sliding straight over the piston and back out of the engine. The end result is a sucking action that pulls the fuel into the engine faster, having similiar effects to a turbo or other forms of forced induction. The dimensions for the different sections of the exhaust have to be the right measurements to be tuned to the engines size. So you cant just put on any old exhaust. Here is a good animated diagram that explains the function pretty well:
http://i258.photobucket.com/albums/hh279/fastboy9/two-stroke_c.gif
I have put a pocket bike exhaust (tuned to 49cc) on my 59cc (60cc happy time) engine and it works quite well, I have the same one as Ghost0, heres the thread:
http://www.motoredbikes.com/showthread.php?t=7800
What I would recommend is to buy a pocketbike exhaust, it is possible to tune it as close as possible to your engine, this is all done by the header length, the pipe from the engine to the expansion chamber. The length will determine where the powerband (where there is an increase of torque at a certain rpm range). The shorter the header pipe the higher in the rpm range the powerband will be (more top speed) the longer the header pipe the better low end torque (faster acceleration).
You can experiment the header length by using a silicone tube and hose clamps, by pushing the metal pipe on the exhaust pipe into the silicon pipe further you will increase your top end. This is how you will tune your exhaust to your engine, once it is tuned how you want it you measure the header length and weld up a pipe for it (brazing copper tubing can also be used). Ghost0 found the optimum header length to be 12 1/2 inches for that particular pipe. I would start from there and start shortening it until you are happy.
The sound is a lot deeper and alot like a dirtbike and the pull is so much nicer! Most 2 stroke tuners will agree that 45% of the engines power potential is in the exhaust design.
Sorry about the long post but I hope it will give you an insight into 2 stroke performance exhausts.
AndyInchVille of Kings sprockets was manufacturing tuned pipes for the happy time engine, and Santa Cruz Scootwer Works (SCSW) pipelyne in san jose were making them too. Theres a thread in the 2 stroke engine section with both Andy and a guy from SCSW offering them:
http://www.motoredbikes.com/showthread.php?t=17109 to be honest if I had the moeny I would get a ready tuned one, will look much cleaner, save a lot of hassle and will be more powerful.
I definetely recommend it
Fastboy
