Performance exhaust

sparkwizard

sparkwizard

#1
#1
I know, expansion chambers are the way to go for performance. However, they need to be custom designed for the engine and a certain RPM.
That's pretty easy if you have a YZ250 or some common platform, but what about us engine swappers?
I have been looking at motorized bicycle junk that claims to "go better without too much noise".
I have funnels, recently purchased a megaphone from a member here, but there is a difference between free breathing exhaust and a chamber.
Header pipes from 4 stroke 212 junk do NOT work well on 2 strokes. I have been looking at performance "race" chainsaw parts.
Has any of you ever messed around with "tuning" the exhaust on old 2 smokers? I'm planning to try making one of these. I'd like to make it adjustable, for testing purposes. Please tell me if you have any experiences with anything like this. Thanks, Dave.
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nightgrider

nightgrider

Well-Known Member
#2
#2
I'm buy no means a 2 stroke expert, but you are dead on with the expansion chamber and performance. Maybe looking into performance exhaust for mopeds. I know there is a lot of options out there and are popular to build. I know there are "performance" kits for the bike engines, but unfortunately I don't have hands on experience.
 
sparkwizard

sparkwizard

#3
#3
My problem is I have a 100 cc engine that makes power at about 34-3800 RPM, and all of the cart and motorcycle engines run at much higher RPM.
Actually, I have several of these old smokers and I would like to harness some of the noise coming out of them, if possible.
 
t555trailblazer

t555trailblazer

#5
#5
The above post^^^ was from an old thread when I was building a Chrysler Power Bee 700. This fellow had some great experience. I remember talking with him about doing the mathematic formulations to come up with the proper size expansion chamber, cutting the shape out of sheet metal, welding it together and then use pressure washer style Hydro forming. Don’t know if he’s still around, it was back from 2017
 
Triley41395

Triley41395

Well-Known Member
#6
#6
t555trailblazer said:
The above post^^^ was from an old thread when I was building a Chrysler Power Bee 700. This fellow had some great experience. I remember talking with him about doing the mathematic formulations to come up with the proper size expansion chamber, cutting the shape out of sheet metal, welding it together and then use pressure washer style Hydro forming. Don’t know if he’s still around, it was back from 2017
Click to expand...
Last time on was 2017 also Screenshot_20240522_153929_Chrome.jpg
 
cl350rr

cl350rr

#7
#7
Here are some pics of the chamber I built for my FS-509, the critical measurement is length from the piston to the middle of the converging cone. the rest you can get creative with. I planned this for a top speed of 6000-6500 rpm, not knowing what I would be able to get out of the engine. as it turns out it is exactly where the power peak is but the engine can do better, it is a bit long and I will be removing a few inches of pipe from the center (shorter pipe = higher RPM range where the pipe works).

please overlook any unsightly welds :rolleyes:

It is a side bleed with the end pipe coming out of just forward of the center of the belly, it is a lot quieter than an end bleed with no loss of power.

This pipe was made from pieces of a Chinese pipe sold on Amazon, along with some bicycle handlebar tubing and a few bike frame pieces. works way better than i had hoped.

I think it goes without saying, I don't build show bikes
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sparkwizard

sparkwizard

#10
#10
Since we are learning, do you have any idea how to adjust for RPM range?
My Jacobsens are old, low RPM high torque smokers.
The stock big heavy mufflers are quiet, but the engines take their time gaining RPM, even with a Tillotson carb.
Big heavy muffler also sits right where I want to put my foot.
With a piece of 1 1/2 inch exhaust pipe welded to a home made flange, it revs quicker, but there is no melody to it.
I would like to make some pretty sounds and maybe a little more power.
They are 100 cc and they were governed around 34-3600 RPM. I don't want them to scream but some noise is better than no acceleration.
 
cl350rr

cl350rr

#11
#11
The measurement I mentioned above is key to the RPM where the pipe works, the distance from the piston face (inside the exhaust port) to a point roughly half way down the final cone. It is based on the speed of sound as you are using sound pulses to do the work. There are tables online that help, I did a lot reading before I made the pipe.

If your engine has the raised wall on the piston top, I chamber may not work as well with it.
 
cl350rr

cl350rr

#13
#13
Well one way to find out is to build a pipe for it and try it.

if you have not already, you should read
2 stroke performance tuning by A. Graham Bell
and/or
2 stroke tuner's handbook by Gordon Jennings

both have a lot of info on exhaust systems
 
markus

markus

Well-Known Member
#17
#17
I did a pipe about 10 years back, Nothing too extensive Never got the bike to run much faster overall (which was fine due to the size of the bike 30mph was pretty fast on 8" OD tires!) but I could adjust stinger placement (could slide it in and out) and was able to adjust and gained more power in the mid range than what I had so that was a win and All I really wanted at the end of the day was an expansion chamber pipe on it cause I thought it would look cool :) It was fun, Still needed at least more length pre chamber, but I was pretty happy with it.

Heres the link: Tuned pipe for the Flee

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sparkwizard

sparkwizard

#18
#18
Thank you, @markus , I have been thinking about this, and I like the adjustment before welding idea.
I can make a little trombone slide and try adjusting it and clamping it before I decide where to weld it.
What is that engine?
 
markus

markus

Well-Known Member
#19
#19
sparkwizard said:
Thank you, @markus , I have been thinking about this, and I like the adjustment before welding idea.
I can make a little trombone slide and try adjusting it and clamping it before I decide where to weld it.
What is that engine?
Click to expand...

it was a 43cc engine and it was Japan made is all I can remember of it, MBW made those bikes in the early 2000's I think it was a 2001
 
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