Eliminate the Muffler

C

Cycofast

New Member
So I realize that I'm relatively new to the world of motorbicycling, but I'm fairly well grounded in thermodynamics. What I'm getting at is removal of the muffler on my chinese kit engine to maximize efficiency. The only down side that I can think of would be the ridiculously loud noise as I roll down the street. If you think about it, this might a) create awareness for cars and b) make my bike sound like a real motorcycle. Of course there is the Police factor, but we'll cross that bridge when it happens.

Also a straight pipe exhaust may be an alternative to no muffer at all.

Your thoughts?
 
These engines need back preasure, Without it alot of the fuel would just blow through I thought?????? Leading to a lack of power ??????
 
Is this really true? I have seen some aftermarket mufflers that have been elongated; wouldn't this effect the "back pressue" ? I guess what I'm saying is that if P and V are proportional, wouldn't the longer muffler negatively impact the P if back pressure was necessary?

Thanks for the feedback.
 
Cycofast said:
Is this really true? I have seen some aftermarket mufflers that have been elongated; wouldn't this effect the "back pressue" ? I guess what I'm saying is that if P and V are proportional, wouldn't the longer muffler negatively impact the P if back pressure was necessary?

Thanks for the feedback.
Click to expand...

Would V = Volume and and and P= Police
 
2 stroke engines are very sensitive to exhaust pressure, size and shape. Because they have no valves like a 4 stroke, the exhaust if built correctly, will act like a valve and increase performance over no exhaust at all. 4 strokes on the other hand pretty much could care less about their exhaust as long as it is not restricting flow. So by eliminating your exhaust you will not only decrease the performance of your engine you will not make any friends in the community.
 
Keeping them quiet is the best policy. If you upset to many people, the next thing you know laws change, and not in your favor.
 
No muffler= great wide open full throttle performance, no idle, very bad throttle transition from idle to wide open or anywhere in between.
 
Think of a mufflers exhast like an ocean wave. When it exits the muffler, a wave of exhast re-enters as the piston drops, sucking it back in the chamber and this adds to the pressure. Its the pressure the forces the piston down again causing power. So a muffler can do more than just muffle.
 
when my baffle fell out, there was more top end, and an increase in throttle response. my bike still idled fine, but that's probably because i blueprinted and ported the motor, so it could take advantage of the free-er exhaust flow.

it was waaaay to loud for the streets of so cal, though. it sounded like a dirt bike. just sitting at a light had everyone in their cars giving me the stinkeye.

i'm still thinking up ways to make an adjustable baffle system, kinda like a supertrapp muffler, but that's not really high on my to do list right now.

i'd love to make it whisper quiet without sacrificing any power...
 
Cycofast said:
So I realize that I'm relatively new to the world of motorbicycling, but I'm fairly well grounded in thermodynamics. What I'm getting at is removal of the muffler on my chinese kit engine to maximize efficiency. The only down side that I can think of would be the ridiculously loud noise as I roll down the street. If you think about it, this might a) create awareness for cars and b) make my bike sound like a real motorcycle. Of course there is the Police factor, but we'll cross that bridge when it happens.

Also a straight pipe exhaust may be an alternative to no muffer at all.

Your thoughts?
Click to expand...
As others have pointed out, if your engine is a 2-stroke, it needs a muffler. The muffler actually helps the exhaust get out faster than it would otherwise, believe it or not. You would be wise to look around for topics about 2-stroke muffler tuning and mods. Tuned 2-stroke exhaust pipes/mufflers start out thin, flare out to a fat section and then reduce down to a thin section again.

Engineering Acoustics/Sonic Supercharging of 2 Stroke Engines - Wikibooks, collection of open-content textbooks

......

If your engine is a 4-stroke, then yes, you can run it with just a short straight pipe, or even no pipe at all--just exhaust blasting out the cylinder head opening--because 4-stroke engine use the piston to actually push the exhaust out. The muffler on a 4-stroke may slightly increase flow (on a multi-cylinder engine with a properly-made exhaust header) but mostly just reduces the noise.

Do note that the vintage board-track cycles had the pipes to guide the exhaust away from the riders' legs.
~
 
You could use a longer pipe and a straight threw non restrictive muffler,like the lawnmower ones or you can mod your stock muffler. So yes it needs a pipe and muffler but it dosent have to be a restrictive one.

A adjustable muffler would be nice.
 
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Ok... I think I understand what is being said here... so am I correct to assume that if I put on an expansion chamber then come off the back of the expansion chamber with a short pipe and muffler I should be OK???

Or will the extra pipe, free flow muffler etc. lower the backpressure too much?

Hummm....
 
have you ever heard these little motors without a muffler? Geezz! My chopper had just a straight pipe from Barry and it was awfull loud!
 
The pressure wave keeps the mixture in the cylinder somewhat, but it does not push the piston down, that's from the combustion.
 
I gotta go with the quiet option....I am going to use my bike to commute this year-I get home from work at 4 AM-I really don't need to tick off my whole neighborhood :-)
 
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