Can we fabricate our own expansion chamber?

HOLY CARP!!

i took the bottom of the muffler off. louder but not too loud, i asked around. it sounds great, imo.

but OMG, this bad baby has a strong "model-airplane" buzz all the way to top-end, then it only cuts out because it's rolling as fast as it's gonna...well, for now, that is.

next: bigger jet :devilish:
 
well all this expansion chamber talk is getting me stoked to go to the exhaust shop my pal owns and build one i am familiar with the program and with expansion chamber design.
the free flowing exhaust thing is not what we need btw
theres a lot of misconceptions on this subject it seems..

the expansion chamber is tuned to the engines exhaust pressure waves. some provide one powerband some provide up to 3 or more depending on the design...

The way it works to create more power is simple to explain but hard to create perfectly..
The pressure waves bounce back at exhaust port keeping unburned fuel from escaping as eaisly into the exhaust and raising cyl filling .. backpressure this is not.

put simply it is a reflected pulse from the engine..the design on the chamber itself decides where this effect is most efficient. the reason a tuned pipe can create more than one powerband is rather complex as the reflected pressure waves can be timed right at more than one rpm giving the effect of multiple powerbands.

with proper design a tuned pipe can be made to increase power over a broad range of rpm and is therefore not just a racing thing as it can be very street handy. also u can put a muffler on the end of a tuned pipe and not change the preformance of it much and still be reasonably quiet.

so plz plz do not just remove those mufflers.. it may help a little but theres better ways to make more power than pissing people off with the sound of our bikes ...

i for one know that when too many noise complaints are made about such an unusual vehicle, laws tend to change in the complainers behalf.
 
well, jaker, i enjoy a fairly remote location so i also enjoy a bit of auditory freedom :p your point is a valid one tho 8)

now, back to the OP: do you think there's a "better than nothing" configuration that would fit in the same space as the muffler? i'm guessing the wrong configuration could in fact hinder overall performance?
 
Just quick note,

grubee have an expansion chamber allready made up if people have actually taken the time to view there webpage

but on the other hand people might want to experiment too

Chieflets
 
i lived on the grubee website when i first started shopping for an engine, never could actually find that pipe available anywhere. dennis foster has plans to make it available this year but he can't say when. he also said it requires a lot of extra space in front and hits some tires on some bikes.

good advice tho...i agree that everyone should read an entire site before getting involved or criticizing the admin.
 
Yeah I've just now done a good bit of reading on tuned pipes, very interesting and make a whole lot of sense. I totally understand why opening up my exhaust has now caused my engine to cut out at the higher rpms. I'm just pissed I don't have the resources to create my own exhaust(s), and try them all out to see the differences in power.
 
Putting the data into that pipe calculator is giving me tuned lengths of up near 180cm, it's the relatively low rpm of the motor that is the biggest problem.

I am working on a small chamber with a proper packed silencer, pics and report to come.
 
Making the chamber specifically for a particular engine is the optimal solution
for making power but I must admit that I tossed in the towel on that one
(design is fairly easy but actual Fabbing and bending the metal proved too much for me)....Instead I opted to find a factory chamber / silencer and custom fabbed the header to tune the assembly....Not 100% optimal BUT Really Really Good!!....Maybe this and sprockets! Hmmmm
Andrew
 

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I think this pipe is the best for the typical 50cc-70cc unit for off the shelf, inexpensive and requiring the lease amount of modification.
http://www.davesmotors.com/store/product1617.html
Some mods will be required but it will be a huge improvement over stock. It has a 1" diameter tube so it will mate perfectly to the current exhaust header portion. Because it was not made specifically for the motor/carb combo (70cc China unit) some tuning will be required. Depending on many variables, gear ratio especially, you will either need to increase or decrease the distance from the exhaust port to the end of the pipe. The shorter the pipe, the more top end and the longer the pipe, the more bottom end. If I had to guess, since the pipe was made for a 49cc engine, I would start with it longer and shorten it an inch at a time until you reach your desired results. I would start by cutting a stock China pipe about 4" from the head and attach the new pipe. You can use fiber reinforced silicone tube with hose clamps for your tests so you don't have to weld it every time. You can usually get the tubing from most auto parts stores or performance shops. It is typically blue or red. I know I will be buying one as soon as I get my moto-bike complete.
 
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