Expansion Chamber

[eDJ]

Check out some of the motorcycle dealers. Often they sell aftermarket performance parts and accessories including expansion chambers and silencers for their line of dirt bikes. I've bought bags of silencer packing at those places.
One friend of mine bought a damaged glass pack muffler at a muffler shop and cut it open to get the fiber glass packing out of it. I think he gave $5 bucks for it and he got all kinds of packing out of it.

 

[ran49]

Well I finally got around to installing a pocket bike expansion chamber exhaust pipe similar to what Ghost0 suggested on my Dax 70cc and I have to say this is without a doubt the the largest performance boost I've gotten from any of the mods.I've done.Thanks Ghost0.
I just switched from a 44 tooth sprocket to a 40 tooth and was thinking about switching back due to the loss of low end torque(ridiculously heavy pimped bike)
Well now it seems I've got it all with the 40 tooth,at least 1 mph higher top end with expansion chamber,but a large hill that would bog me down to 11mph I now climb at 18mph.I highly recommend this mod,just wish I'd done it sooner.Ron

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[Ghost0]

ran49,
Nice job on the install but if I can make a suggestion? Shorten your header. It appears that you have enough room to raise your pipe without hitting the frame, pedals etc. I find the optimum distance for that pipe on a 70cc is about 12 inches from the exhaust port to the beginning of the expansion chamber. You won't lose much bottom end but you will gain a ton of top end.

 

[ran49]

Ghost0:
All along I was thinking that silicone tubing had the added benefit of being adjustable but I couldn't find any around here.I'm at about 13" now.I'll cut an inch out and give it a try.I silver brazed the pipe together thinking it wouldn't hold up too the heat but so far so good.Anyway it will be easy to pull apart.Thanks again,Ron

 

[Weedylot]

Good animation on the expansion chamber. I've tried to explain its benefits in the past by describing it as "scavenging exhaust pressure" which is a poor description. I've found some sources (Delottoro and Morini) for pipes and chambers for 50cc motors on some of the moped sites.

 

[jasonh]

So would an expansion chamber have to be really rounded like most of these commercial ones, or could they be very square and angular? Seems like if they can be angular, it wouldn't be hard to fab one up with access to something to cut and weld metal. (this is in regards to the design program previously posted)

 

[FileStyle]

you would want the exhaust to flow smoothly and with sq. or angular you would get disturbance of flow within the pipe.

 

[eDJ]

Somewhere back in this thread I believe someone was asking about the amount of fuel that was wasted by a 2 cycle engine equipped with a muffler. I found some information in a California business publication of the California EPA Air Resources Board today.

It seems about 30% of each scavenging "cycle" is lost with a muffler equipped 2 cycle engine. I don't have figures yet for how much is saved when using an expansion chamber but certainly it is much better than 30%. Clearly the
expansion chamber compresses much of what would be wasted back into the combustion chamber.

You can see this information used in the report here:

Business Information: Clean Air Two-Stroke for Utility Engine Applications Demonstration, BKM

But this information may be general enough for these Chinese engines in the kits presently available.

 

[MrLarkins]

where can i get a pocket bike expansion chamber? should i look around at local cycle shops? are they most likely to carry them?

would something like this (47cc 49cc Pocket Bike HP PERFORMANCE Exhaust Pipe part - eBay (item 150160565919 end time Sep-05-08 09:13:10 PDT)) work?
or is that one too small?

 

[Pablo]

That is essentially the one I have.

You can make it fit. We have a kit in the (slow) works.

 

[threespeed]

Ghost0, what type of pipes are you using and where can I get one?

 

[Ghost0]

Here is one like mine on ebay.
47cc 49cc Pocket Bike HP PERFORMANCE Exhaust Pipe part - eBay (item 150160565919 end time Sep-05-08 09:13:10 PDT)

 

[Norman]

I bought one last night when it gets here I'll fire up the saw and the gas welder and see what comes out of the smoke and fire. I'll bet it won't be chrome anymore. I noticed that it comes with a knock off K&N type filter with a stack. I wonder what I can do with that? evil grin.
Norman

I'm gettin lazy might be easier than rolling my own like I've been doing at least a lot quicker. should be better than a home rolled.

 

[lennyharp]

I ordered one from them the day this was posted by Jim. If there are ways to make it work best, better or worse I definitely am interested. I want to mount it on my slant 50 with a SBP shift kit so I have a really smooth running system. I was surprised to see the filter and stack and don't know what to do with it but may figure something out.

 

[Norman]

I maybe wrong but I'm thinking a guy can use that mount and V stack with filter on these bike engines with out too much mods. but then I've been wrong before. Mr. lathe might come in handy on it to make it fit.
I also need to decide which bike to put it on.
I need some sound effects of lord vader with heavy breathing
Norman

 

[Pablo]

Norman you are an animal. I mean that in a good way.

Keep us posted on the pipe.

 

[ran49]

The filter that came with my pipe,same one I imagine,was easy to adapt using the the round plastic grid that holds the foam filter in the original filter.Cut the two tabs off and it Fits right into the chrome rim on the front of the filter.I cut out a gasket but it may not be needed.You have to drill the chrome lid on the back for longer screws and use large washers or a back up strip so not to dimple the lid.Seem to make a difference but probably not too hot in the rain.Ron

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[Norman]

looks like you couldn't use the v-stack? you all are maybe going to see some really strange mounting of my pipe and carb by the time I get r done and yea I'm sometimes an animal and I thought that was funny as h$ll and like it.
big $hit eating grin with the heavy breathing and the theme song of lord Vader playing in the back ground with Inna god of davida being played backwards, me cussing, screaming ,crying, frothing at the mouth and having a good time cutting the new pipe into little bite size pieces tearing up the new air filter and Rufus sharping his claws on the rear tire.
It's a great day.
Norman
I think I need to thank Ghosto for posting on where to get the pipe I ordered it Monday and got it today that was fast!

 

[ran49]

I'm guessing by v-stack you mean that nicely machined funneled connector.Ran out of room!I'm thinking of attaching a curved hood on the back in case I get caught in the rain.Maybe act as an air ram or possibly a rain ram. lol.Anyway between the expansion chamber and the filter I feel like I have 20% more power,give or take 5% for placebo effect.Ron

 

[Norman]

That stack will fit the carb perfectly I relieved the choke bolt by drilling the back side of the stack where the chokes bolt sticks out a little she bolted right on I did put some sciclone gasket goo around where the stack and carb meet.
I wouldn't worry about moisture on the air filter unless there was a toid floater rain storm my airplane has a foam air cleaner and I don't go around the rain when I'm flying so far it hasn't quit, it eats the rain.
I've cut the exhaust pipe into pieces and going to go weld it up here in a little while.
My carb with the stack will not clear the frame but I'm making one of my offset intake manifolds so I can run the stack and air cleaner.
Well I better go to play.
Norman