Adding an expansion chamber to a poo poo pipe?

pod

New Member
Oct 16, 2010
2
1
1
Minnesota
I guess I'm a bit stubborn. I've got a 66cc Happy time on a Cranbrook frame, and I have a poo poo pipe on it's way right now. I really like the look of the long poo poo pipe on the Cranbrook, and want to keep that aesthetic

Now, if I ordered a cheap banana expansion chamber, drilled out the end and welded in the pipe, does anyone think that there will be a net improvement? I throw out the cheap banana because it's so cheap that I don't mind hacking one up. Is there a better choice for not much more?

I'm also shooting for low to mid range torque, and not for ultimate speed. If that helps
 
  • Like
Reactions: Dan

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,549
238
63
living the dream in southern california
With the long header pipe on the poo poo, it won't make any performance improvement. It'll just change the sound.

I know, because I've done it.

X chambers work off waves, and the wave will dissipate through the long head pipe.
 
  • Like
Reactions: Dan

pod

New Member
Oct 16, 2010
2
1
1
Minnesota
I might have been confusing, I meant to bolt the banana expansion chamber directly to the motor, and where the Normal exhaust leaves the banana chamber, cut a hole to install the end of the poo poo pipe, so the exhaust ends up at the back of the bike, with a muffler.

In that orientation wouldn't the expansion chamber still be able to do it's job, and reflect the pressure waves?

Also where in the power band do those banana pipes pick up?
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,549
238
63
living the dream in southern california
That should work, the poo poo would be an extra long stinger, which would affect it some, but no way to know unless you tried both ways, with and without.

Dunno about the powerband, but I've heard of people having surprisingly good results with it.
 

Benlol635

New Member
Sep 1, 2017
2
2
3
22
Hey could you let me know if your plan works i had the same idea as you but haven't had the money to test it out
 
  • Like
Reactions: Dan

Dan

Staff
Staff member
May 25, 2008
12,775
106
48
55
Moosylvania
Purty awesome. Especially if it helps with the power range you want. Would look, sound and be cool.

Looking forward to hearing how it works out, Pod.

Ride safe!
 

KCvale

Well-Known Member
Feb 28, 2010
3,967
52
48
Phoenix,AZ
I got one of those Sick Bike Parts expansion chambers and it has about a 17" header and it makes a big difference for the low end but I wouldn't want to go any longer.
You have to understand how expansion chamber exhaust really works.


It's all about timing, follow the green fuel.

The length of the header is everything, and sick bikes pipe in spot on for a 48cc, for a 66cc you want to cut that short copper pipe connecting the elbows in half so the elbows are flush.

Nothing add after that, providing it flows free, matters.
This was a 'quiet screamer'.



and this was a joke but what the customer wanted.



That pipe did nothing for performance, but it looks cool.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,140
169
63
Santa Barbara, CA
You have to understand how expansion chamber exhaust really works.


It's all about timing, follow the green fuel.

The length of the header is everything, and sick bikes pipe in spot on for a 48cc, for a 66cc you want to cut that short copper pipe connecting the elbows in half so the elbows are flush.

Nothing add after that, providing it flows free, matters.
This was a 'quiet screamer'.



and this was a joke but what the customer wanted.



That pipe did nothing for performance, but it looks cool.
I understand all that. I actually added a few small copper parts to the header which made it come out to about 17" . This is why I said I wouldn't want to go any longer on the header or I would lose the middle because the power range would too low. I gotta say that the expansion pipe on the last picture you posted looks too small to make any difference no matter how long you make the header or how fat the header is.

Even my SBP one is rather small. I purchased it years ago but today I would get a better and larger one. However, the SBP one did make a pretty big difference for the mid and low end with a 17" header. With stock I went 0-20 mph in about 3-5 seconds, after I put it on I got up to 20 mph in 1-3 seconds. It was a noticeable difference. If I shorten the header I would probably get more top speed but I didn't want that. This thing already tops out at about 36 mph with a 40 tooth sprocket, I wanted the bottom end!
 

KCvale

Well-Known Member
Feb 28, 2010
3,967
52
48
Phoenix,AZ
I gotta say that the expansion pipe on the last picture you posted looks too small to make any difference no matter how long you make the header or how fat the header is.
Heehee, ya, it was just to get his exhaust to the rear and look cool, it provided no noticeable performance improvement.