Expansion Chamber Mods.

Outrunner

Outrunner

New Member
I've been experimenting with different ex-chambers and mufflers, just
to see for myself what the results would be.So far I've had a total of 6
different exhaust pipes mounted to my bike. Here are 3 of the expansion
chambers that I've tested. So far the best one has been the short pipe,
followed closely by the rear mounted ex-chamber. I'm really surprised
how sensitive this 67cc motor (engine) is to various mufflers (4) and
different applications of pipe length, muffler back pressure, expansion
chamber location and type. I'm going to try 2 more ex-chambers in the
next 2 weeks, and I'll post some new pics and results. It sure is much
more complicated than I expected, and very time consuming due to
replacing and resetting the Mikuni 18 mm carb needle positions, main
jets and pilot jets. But it it is interesting and fun too.
 

Attachments

  • img_0003.jpg
    img_0003.jpg
    86.4 KB · Views: 440
  • img_0029.jpg
    img_0029.jpg
    145.1 KB · Views: 445
  • img_0031.jpg
    img_0031.jpg
    138.4 KB · Views: 438
Last edited:
Your bike is very nice, at least what I could see of it. I built a exhaust from a pocket bike pipe just like the rear mounted one in your pics. The length of the header is most important. Shoot for 12" - 12 1/2" from the cylinder to the start of the expansion chamber. I also added a 4" extension between the chamber and muffler for easy tire clearance. Here's a pic of my pipe. Cool post.

P1010137.JPG
 
Good stuff. I'm thinking pic #1 would not add much perf, if at all. But are you saying this is the best? (cornfused) How did you measure?
 
Has anyone taken the stock exhaust apart and removed the innards and us it as an expansion chamber? I am currently trying this with a old stock exhaust that I have and I intend to find a muffler to put on the snout of the exhaust to quite it back down. I looked inside of the "expansion chamber" of the stock pipe and couldn't believe what I found......a perferated outgoing pipe, a solid return pipe and 4 baffles........how is that supposed to work as a expansion chamber when it is full of stuff that will not let the sonic wave move back and forth! It is just a 4-stroke exhaust slapped on a 2-stroke!

.sno.
 
Pablo said:
Good stuff. I'm thinking pic #1 would not add much perf, if at all. But are you saying this is the best? (cornfused) How did you measure?
Click to expand...

Pablo, the best exh. pipe so far is the shortest one. A very close 2nd is the
long 1/2" pipe with the ex-chamber and stinger on the end. I don't know
why it works so well, but I am checking the speed and rpm with a digital
tach and digital speedo, plus I calibrate the speedo to a fixed traffic radar
sign that lights up with big LED numbers indicating your oncoming speed.
Plus the general acceleration from a 6 foot pedal start.I'm measuring the
pipes to fit the frame and using what I call a " By guess and by golly " trial
and error. I have yet to try two more ex-chambers. One that will go up and
mount just below and to the left of the gas tank and route past the seat.It's
made by SCSW. The other is very similar to the long pipe set-up. Anyway, I
will try as many variations as I can fit to my bike. It looks like I'll have to
remove my center stand to get the proper set-up.
 
Junster said:
Your bike is very nice, at least what I could see of it. I built a exhaust from a pocket bike pipe just like the rear mounted one in your pics. The length of the header is most important. Shoot for 12" - 12 1/2" from the cylinder to the start of the expansion chamber. I also added a 4" extension between the chamber and muffler for easy tire clearance. Here's a pic of my pipe. Cool post.

View attachment 10558
Click to expand...

Junster,
Hey, I like the nice job you did on your ex-chamber. It looks like I will have to
remove my center stand ( I love that thing) in order to fit an ex-chamber so that
it fits AND works!! Thanks for your compliments. BTW, today I bought a oxy- acetylene torch set, so I can do some serious brazing (or damage) on my
modifications.
 
Last edited:
Well remember how the chambers work. The engine end cone is twice as long as the muffler end cone. There is usually a straight center section between them. The exhaust sound wave expands down the initial cone then back to the rear cone where it is reflected back towards the motor. The idea is for the wave to reach the exhaust port in the cylinder just before the piston closes the port. Kinda stuffing some exhaust and energy back into the cylinder just before compression as the exhaust port is last to close. Just opening up the restrictive exhaust is a big help but when you get the header length close so the timing is right is when you'll hear the exhaust note and power really change. It will get a ring, ding, ding, ding. Just like a small dirt bike.

Mine was welded by a friend who's very talented with his wire feed but I'm sure braizing them would be fine.
 
Ya I just ordered a shift kit and a rear kickstand from SBP. The kickstand they have clamps to both the chainstay and the seatstay near the rear wheel. I had to give up my original stand too. The guys at SBP really have it together. My favorite place to order from.
 
Outrunner said:
I've been experimenting with different ex-chambers and mufflers, just
to see for myself what the results would be.So far I've had a total of 6
different exhaust pipes mounted to my bike. Here are 3 of the expansion
chambers that I've tested. So far the best one has been the short pipe,
followed closely by the rear mounted ex-chamber. I'm really surprised
how sensitive this 67cc motor (engine) is to various mufflers (4) and
different applications of pipe length, muffler back pressure, expansion
chamber location and type. I'm going to try 2 more ex-chambers in the
next 2 weeks, and I'll post some new pics and results. It sure is much
more complicated than I expected, and very time consuming due to
replacing and resetting the Mikuni 18 mm carb needle positions, main
jets and pilot jets. But it it is interesting and fun too.
Click to expand...
Here's the latest performance test results of all the different types of
exhaust systems that I tried. Without a shadow of doubt, the best
performance gain along with smooth mid range power is the expansion
chamber made by SCSW. It is a top mount system which allows me to
retain my center stand, which I preferred to keep. I had to solder my
#70 main jet, and re-drill it to about a #60 jet size for the Mikuni 18mm
carb. Now, it has a smooth transition of power from 5-35 mph! Excellent
acceleration too!
 

Attachments

  • img_0055.jpg
    img_0055.jpg
    231.1 KB · Views: 326
Bikedad1 said:
Has anyone taken the stock exhaust apart and removed the innards and us it as an expansion chamber? I am currently trying this with a old stock exhaust that I have and I intend to find a muffler to put on the snout of the exhaust to quite it back down. I looked inside of the "expansion chamber" of the stock pipe and couldn't believe what I found......a perferated outgoing pipe, a solid return pipe and 4 baffles........how is that supposed to work as a expansion chamber when it is full of stuff that will not let the sonic wave move back and forth! It is just a 4-stroke exhaust slapped on a 2-stroke!

.sno.
Click to expand...

I cut the outter tube off and redrilled more holes farther up the inner core tube. I removed the baffles and welded closed the lower core holes (there are now more holes on the upper part than the lower had originally) I then cut the small outlet pipe off flush with the end cap inside end and used a piece of it to add a second small outlet pipe (twin tip) I cut it flush inside too. I welded the large tube back on and stuffed a copper pot scrub pad up unto the lower end of the muffler where the baffle plates once lived and put a small piece of screen (1/8 inch machine wire screen) at the bottom before putting the cap back on to keep the pot scrubber from being blown out over time. The end result; It is quieter, flows like one thats been gutted and retains the catalyst element for emissions (if it in fact even works)
 
Hey guys not sure if im in the right fourm but, i bought the upgrade exhaust and i dont like it can i put the original back on with out any of the insides and just cap the open end off with something with a whole in it? I lost the baffles from inside and the cap, im just worried the exhaust gasses mite stay in the pipe
 
Im worried they mite stay in the pipe and blow the pipe up because i remember reading a fourm about a guy having something similar happen but i cant find the link. Thanks for your time
 
I run a gutted stock exhaust ( poor mans expansion chamber ).. had to move the C clip in the carb down 1 slot but it runs great.. wouldn't suggest it for an urban area due to exhaust note.. it's not really loud, but it is louder than stock
 
Outrunner said:
Here's the latest performance test results of all the different types of
exhaust systems that I tried. Without a shadow of doubt, the best
performance gain along with smooth mid range power is the expansion
chamber made by SCSW. It is a top mount system which allows me to
retain my center stand, which I preferred to keep. I had to solder my
#70 main jet, and re-drill it to about a #60 jet size for the Mikuni 18mm
carb. Now, it has a smooth transition of power from 5-35 mph! Excellent
acceleration too!
Click to expand...

i got to get me one of those carbs im lovin that pipe i got from ya i got all the leaks out and it sounds great the the bike runs fantasic with it. trade you my bike for yours :D
 
You must log in or register to reply here.
Back
Top