Expansion Chamber

[Norman]

Check out my way of mounting the pipe and aircleaner He He!

I'm a sick boy I'm always getting things backwards.

 

[lennyharp]

Okay does this amount to just turning the part that mounts the pipe and carb around 180 degrees leaving everything else the same? This is SICK, and I will be trying this too.

 

[packeryman]

Has anyone tried to modify an 80cc Yahama YZ exhaust system to the "80cc" Chinese 2cycle engines? I have access to one(1989 it was used for motocross)with an 80lb rider it had a power curve you hit at a certain RPM and it really took off.

 

[Norman]

you have to make an intake manifold and an exhaust mainfold. you will also need to modify the tranfer ports form the crankcase and cylinder head turn the piston around backwards along with the cylinder and head new gaskets base, head, intake, exhaust, longer fuel line. Then tweak the carb for it to run good. I'm not sure but I think that if I shortened the exhaust pipe mainifold where it runs from the engine to the tuned pipe it might run better I kept the length the same length as when it came out of the box. the intake filter was nice very little work to get the V-stack to fit and still use the airfilter. this will make the bike very quiet all I hear is the whine from the gears and the intake.
Norman

 

[packeryman]

This sounds like a major project, I am looking at the Yahama 80cc now and the exhaust port is in the front of the engine with the intake to the rear. They have engineered a very convoluted exhaust pipe and expansion chamber before dumping into a muffler about the size of the one on the Chinese. I can understand having to make both an exhaust and intake manifold to adapt to the Chinese engine. Using the YZ configuration, the only problem I see is a hot exhaust by your left leg. They used a good heat shield. My question is why are we redesigning the whole exhaust and intake configuration. I have no experience in 2cycle engines. This question is for real, not to question your experience and knowledge of 2 cycle engines. The only thing I can see is the exhaust and heat shield is futher outside the frame of the bike than one might want. Here is the clincher, would we see a power increase worth the effort or would you just chalk it up to a fun project? I have had many of those and sometimes enjoyed the project more than the expected outcome. Thanks

 

[Norman]

I did the mod. for the fun of it I haven't seen one yet so I decided I'd try it.
The exhaust pipe is tucked in very close to the center of the bike where you would contact it with a leg so I see no need for a heat shield. I'm now going back and will work on the ports to match them up. This bike was very fast before I did the changes, with the changes part of the transfer ports to the cylinder are covered so it isn't as fast but that will change I think
Yes it is sort of a lot of work and not for everyone. I'm even thinking of shorting the straight section of the exhaust. when I got the pipe it was 13" from the exhaust flange to the start of the chamber I'm maybe going to shorten it an inch at a time to see what that will do then I will have to make a new chamber mount as I've welded the mount on to the frame darn it I'll have to cut it off and re weld a new mount.
But first I'll do the ports and see what that does I still need to do some smoothing of the intake too all for fun.
If I can find some tubing that's not stainless I'll make a better intake I might try to make it match the ports on the cylinder and that will involve making the mounting holes inside the intake so I've got all kinds of things to make that will keep me off the streets.
I need to change oil in the Harley so I might hold off for a while as I ain't in a hurry now that I know the backwards thing will work. I'm even thinking of buying a new engine just so I can use it backwards from the get go.
Norman

 

[Egor]

Norman Some of the fastest bikes in the fifty cc class were made to run the exhaust out the rear, it is all about the fit and you could install a velocity stack out in the air stream. Have fun, Dave

 

[wizzizer]

hey ran49, where did you get your pipe?

its my fav so far in terms of size and style. and it seems like i could use the stock pipe as a donor for the header leading into it.

 

[jak stoll]

hookwormrider.... was there a noticable increase in power?
take care
JAK

 

[eDJ]

For those who have come to this thread only of late, we now have a post in the "Classic" section that addresses expansion chambers as an overview.

I've been searching to see if anyone still produces them as they once did when 2cycle bikes were common. Leo Vince hand crafts them but they are "pricey". If a good working pipe for a 50cc were cast to make stamping dies
then sheet metal could be stamped to create the two halves of the truncated cones section and tubing could be bent and all of it robot welded together in a jig in production to get the cost of these down considerably.

Yahoo! Shopping Search Results for Expansion Chamber

Expansion chambers are probably the simplest & least expensive way to add a boost in power that you can feel. A higher volume air filter works well when using a chamber too.

On a 50 to 100 cc motorized bike installation I'd think that routing the chamber upward on a diagonal slope to the rear axle (or further thru a fiberglass packed bolt on silencer) would have it up out of the way of the pedals and be comfortable for the rider. It would look like the old TT pipes of earlier times motorcycles too.

 

[jak stoll]

hey norman
I also noticed when I had the cylinder off of mine that the transfer ports were sorta directional & may need to be re port matched if the cylinder was 180d like you did,,,, I just dident know if you looked at that,,,
way cool though I have to say
take care
JAK

 

[Ghost0]

To me this is the simplest solution there currently exists on the market. It requires the least amount of modification and works excellent. It is also mounted out of the way of burning anything except rubber.

 

[jak stoll]

here is my first attempt

I cant really tell any difference
I think its way too big & poorly executed I was rushing
take care
JAK

 

[jasonh]

To me this is the simplest solution there currently exists on the market. It requires the least amount of modification and works excellent. It is also mounted out of the way of burning anything except rubber.

So when will it be for sale?

 

[Ghost0]

It is in the works but not the first priority for SBP. Until then if you are interested I can point you in the right direction. The installation has been covered elsewhere on this site.

 

[jak stoll]

I went about 35 miles tonight & either I dident fill the tank enough (unlikekey) or the pipe has my milage way way down (overscavenging) I mean I ran out of gas 1/2 gallon in 35 miles its a wonder it even ran
it seems to run better in the upper mid range but off the line its a complete dog
Im going to make the chamber much smaller tomarrow
take care
JAK

 

[[email protected]]

The reason it is sputtering is because your pipe has been altered from how it was designed. The distance from the exhaust port to the beginning of the expansion chamber is a very critical dimension. If this distance is changed the pipe will not work properly. I am sure it works better than the stock pipe but unless tuned correctly it will not offer the performance advantage that it should. These engines have a powerband in the 4 to 6 thousand rpm range. To properly tune a scooter/pocket bike pipe for one of these engines, the recommended distance from exhaust port to the start of the expansion chamber is about 12 inches. This can be altered plus or minus an inch or so to correctly tune it to your gearing and riding style. The attached photo illustrates how to measure your header length.

where did u get ur expansion chamber from!? or did you make it?

 

[Ghost0]

This is the same one I use, you can get it a little cheaper on ebay.
47cc Pocket Bike Performance Pipe(parts,accessories)

 

[jak stoll]

so here is the second attempt
it will look better when its painted up
have a great weekend
JAK

 

[michael]

This is wifes set up. It really hauls!!!