Quieting Down A China Girl Motorized Bicycle???

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ProDigit

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Mar 27, 2013
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Re: Quieting Down A China Girl ???

I'm quite sure that the exhaust gasses that enter the muffler are much hotter than 200 degrees.
If you cut off the end part of the muffler, and mount a hose the size of the muffler, you won't have much sound damping.
If you mount the hose at the exhaust tip, you'll increase back pressure, and decrease performance.
 
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ProDigit

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Re: Quieting Down A China Girl ???

Exhaust gasses at the cylinder reach temperatures of ~1600F.
The exhaust gasses often on motorcycles (like 250cc aircooled Rebel Honda's or similar), often can decolor the metal pipes because of heat (giving them a rainbow pattern of blue/green/yellow)

After the exhaust pipe, the mixture enters the muffler, where it cools down a lot more.
Quite often the exhaust fumes are still over 200c, especially with a small muffler like the one used on most bicycle engine kits.

However, if you have welding skills, and can extend the exhaust pipe, and mount the muffler near the rear wheel sprocket, the gasses may be cool enough to try a rubber hose.
 
Master-shake

Master-shake

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Re: Quieting Down A China Girl ???

I was thinking of using a hacksaw to cut the muffler off after the first bend and attaching there. The 1200 degree mark looks a little high to me I would think that a smaller cc engine would make less heat. A radiator might help but at that point I might as well just buy a torch/flux/solder, and do like that one guy did in the post "the silencer."

http://motorbicycling.com/showthread.php?t=34834

I was going to like the look of the rubber on my bike too :(

I guess I'll get the logistics of that silencer and modify it to look different. A couple of 45's and 3/4" brass pipe are all I got so far. This might help my steam-punk appeal now that I think about it. I already changed out my choke lever for a 15t off an old shimano. Looks ok, I'm still trying to position it just right.
 
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lowracer

lowracer

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Re: Quieting Down A China Girl ???

I have installed 2 stock china girl exhausts onto 2 different engines.
It definitely has quieted down my Tanaka 47r & Tanaka 40cc to very 'acceptable' sound levels. The stock canister mufflers are loud & don't allow the engines to reach higher rpm ranges.
I was running a pocketbike expansion chamber pipe, which is a bit louder than the china girl pipe, but provides a bit more top end provided you run ~12" of header pipe before the expansion begins.
The china girl pipe needs to be braced to stay tight (prevents loosening of the manifold bolts). I also like to run header tape the whole length of the pipe to prevent another burn....doh!
-Lowracer-
 
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Master-shake

Master-shake

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Re: Quieting Down A China Girl ???

seems like we are going to need to include this into our knowledge base.

Two-stroke engines depend upon the design of their exhaust system for their usable power band and maximum power output. Waves of positive and negative pressure travel back and forth in the exhaust system. These positive and negative pulses are created by various components designed into the system and travel at near the speed of sound, depending upon the gas temperature. The engineers use these negative and positive waves as valves for the exhaust port.
Click to expand...
So "The Silencer" hypothetically could be manufactured to raise or lower not only horsepower but Noise as well depending on how we play off the harmonics of our little two strokes. this principle may be why "Boost bottles" work or don't. I'm no expert and neither are many of the hobby DUI transportation seeking people. I can only assume that our engines will only be as balanced as we make them, especially if we go into "special fabrication" with things like the silencer or custom boost bottles and their placement down to the degree.

We need a baseline "Quiet this china girl!" enthusiasts. We're all running stock right now, How about we all try the same mod and see if we get the same result.? I know one of you is running an Onyx so we might be the perfect candidates for a test group.

I nominate myself to be the control... lol

.cs.
 
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ProDigit

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Re: Quieting Down A China Girl ???

2door said:
Not being argumentative but just curious where you got that temperature estimate.

You might find some of this interesting> http://www.challengers101.com/ExhaustGasTemp.html

Tom
Click to expand...
The link you quoted, said that temperatures in the permissable range are"1200 F to 1300 F range". That being said, Wikipedia says that temperatures for a (regular) engine can exceed 1600F (due to engine running lean).
Now, I'm sure on a tiny 2 stroke engine we won't see 1600F temps, but it is still possible.
 
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ProDigit

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Re: Quieting Down A China Girl ???

Master-shake said:
seems like we are going to need to include this into our knowledge base.



So "The Silencer" hypothetically could be manufactured to raise or lower not only horsepower but Noise as well depending on how we play off the harmonics of our little two strokes. this principle may be why "Boost bottles" work or don't. I'm no expert and neither are many of the hobby DUI transportation seeking people. I can only assume that our engines will only be as balanced as we make them, especially if we go into "special fabrication" with things like the silencer or custom boost bottles and their placement down to the degree.

We need a baseline "Quiet this china girl!" enthusiasts. We're all running stock right now, How about we all try the same mod and see if we get the same result.? I know one of you is running an Onyx so we might be the perfect candidates for a test group.

I nominate myself to be the control... lol

.cs.
Click to expand...
The best exhaust is a free flow exhaust (just a pipe).
However a pipe is loud. And the high frequencies are more damaging to the ears, than the low frequencies. That is why old style mufflers had fiberglass in them, to muffle the higher frequencies.
The lower frequencies are less harmful to the ears.
The more you muffle the sound, the more back pressure you create. The more back pressure, the less exhaust can get out of the cylinder, and the less exhaust gasses exit the cylinder, the less fuel/air mixture gets into the cylinder, causing a degration in performance.

Exhaust mufflers don't improve performance, they degrade performance. A good exhaust muffler can degrade performance less than a bad one which in turn gives a performance increase relative to the bad exhaust muffler.

But usually the better performing exhausts, give more (harmful or hard/sharp)noise than the lower performing ones.
 
2door

2door

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Re: Quieting Down A China Girl ???

ProDigit said:
The link you quoted, said that temperatures in the permissable range are"1200 F to 1300 F range". That being said, Wikipedia says that temperatures for a (regular) engine can exceed 1600F (due to engine running lean).
Now, I'm sure on a tiny 2 stroke engine we won't see 1600F temps, but it is still possible.
Click to expand...
It also says that at 1600 there is potential for engine failure. I'm sure we all want to avoid that so it's a good argument for keeping to the rich side as opposed to going as lean as you can go. Again, spark plugs will tell you a good deal about where you're at.


As for mufflers, I'm having good luck with a straight through glass pack that I built for my latest chopper. It's as quiet as a stock muffler but there is a noticable power increase over the kit supplied pipe and muffler combo. It took some work and fabrication but the effort seems worth it. I don't like the looks of the expansion chamber style and wanted something with a more motorcycle look. I wasn't looking for top performance.

Tom
 
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ProDigit

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Re: Quieting Down A China Girl ???

2door said:
It also says that at 1600 there is potential for engine failure. I'm sure we all want to avoid that so it's a good argument for keeping to the rich side as opposed to going as lean as you can go. Again, spark plugs will tell you a good deal about where you're at.


As for mufflers, I'm having good luck with a straight through glass pack that I built for my latest chopper. It's as quiet as a stock muffler but there is a noticable power increase over the kit supplied pipe and muffler combo. It took some work and fabrication but the effort seems worth it. I don't like the looks of the expansion chamber style and wanted something with a more motorcycle look. I wasn't looking for top performance.

Tom
Click to expand...
Most of the sources we've brought in where for 4 stroke engines.
with 2 stroke engines, the engine has half the time to cool down, so it might reach hotter temperatures than a 4 stroke, despite being a smaller engine...
It's all a bit relative to a lot of surrounding factors.

On a boat, those rubber hoses are under water, and directly cooled by water.
It's a totally different scenario in the air!

Mufflers:
if you're into welding, you can actually mount a 300cc 4 stroke exhaust onto the exhaust pipe.
It'll work, and work well, because all you need is an exhaust pipe. And the larger the muffler, usually, the better muffling it does, while the better free flow it has.
Smaller mufflers have a hard time getting low levels of back pressure, but they do muffle higher frequencies better. The smaller the muffler, the higher the frequencies they muffle.
For that reason, the larger the muffler, the more it muffles the sound into a low sounding BOP-BOP to RWRWRWRW , rather than a chainsaw EEEAAANNGGG sound.
 
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Catfisher

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Apr 10, 2010
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Re: Quieting Down A China Girl ???

:rolleyes:

I didn't get the job I had expected to be riding to each day. It really sucks because I know I was by far the most qualified and experienced applicant. But when the interviewer is half your age, you never know how they will respond. I left the interview believing I had nailed it. No one at the huge company will return my calls, so I can't seem to get any answers or reasons.

For now things are back on hold as I am trying desperately to save my house from the tax purchaser's.

Given the area I live in and my need to be unnoticeable I hope to go electric someday. This post from Paul really did a lot to convince me.

Magic Pie 3 on Trek 3500 disc bicycle - Motorized Bicycle - Engine Kit Forum
http://motorbicycling.com/showthread.php?t=40212

But if the need for the bike arises before the funds for an electric are available I will try a modest China Girl.

Thanks to all who contributed to this thread, I learned more and was entertained at the same time.

.flg.
 
Dan

Dan

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May 25, 2008
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Re: Quieting Down A China Girl ???

Wow CatFisher, sorry to hear Buddy.

Please keep posting how you are doing.
 
mark880088

mark880088

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Re: Quieting Down A China Girl ???

Hey Catfisher I'm in Springfield and they are legal here with no license. I put thousands of miles on mine with no run ins with the police. I do ride responsibly and respectably though. I stop at all stop lights/signs and try to watch my speed. I've never been stopped once, and have passed dozens of cops. Some have even waved at me. This is just my opinion but save your money till you can get a four stroke. The time and money you will spend fixing the two stroke will soon catch up to the price of the four stroke. I found out the hard way lol
 
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ProDigit

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Re: Quieting Down A China Girl ???

What's the gas mileage on those 4 strokes, and why do 2 strokes have such high maintenance that you want to go for a 4 stroke that's over double the price of a 2 stroke?
 
2door

2door

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Re: Quieting Down A China Girl ???

ProDigit said:
What's the gas mileage on those 4 strokes, and why do 2 strokes have such high maintenance that you want to go for a 4 stroke that's over double the price of a 2 stroke?
Click to expand...
Pro,
You'll get differing opinions. Those of us who use and prefer the 2 stroke engines will tell you that reliability is not an issue. We put thousands of miles on our little poppers and don't see the failure rates suggested by the folks who use the 4 strokes. Each type has pros & cons. It usually comes down to personal experience and preference.

Tom
 
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ProDigit

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Re: Quieting Down A China Girl ???

I heard from my friend who's really into 2 stroke scooters, that those engines tend to break when revving them too high. On scooters they are often tuned to race at 10k RPM or more. In such situations, it's not very uncommon to have an input/exhaust valve break, or something go wrong.
However, I seldom hear of stories of breaking 2 strokes on regular tuned machines.
Most of the time, in max gear, 2 strokes won't reach above 8k RPM anyway (eventhough without load they might go 11k RPM).


From my calculations, a 2 stroke bicycle with engine kit is more affordable than a 4 stroke scooter.
I did calculations once, and just on fuel price (where 2 stroke uses fuel and oil), they cost about the same if the 2 stroke reaches 135MPG, and the 4 stroke reaches 100MPG.

However, with oil change for the 4 stroke, both are about on par with each other in gas mileage and oil/fuel fillups.
Generally, 4 strokes are more efficient though, and run at higher MPGs.
The 100MPG value I have,is from a scooter, not a motorized bicycle.

Knowing this, a 4 stroke motorized bicycle very well might be able to reach over 135MPG


One question,
those 2 stroke engines; I have one at my house, but never really looked at it; do they need gear oil too?
If so, which oil?
 
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