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member: xteraco

i got an idea for my muffler, its kinda like.... my muffler has one chamber inside of it.. i was thinking of hollowing the chamber out, and then welding a pipe that goes from my pipe that connects to the muffler straight out the back, so that exhaust doesent build back pressure in the chamber... the pipe that goes throught my muffler would be as wide as the pipe that connects to the muffler

i think this would make it louder, but it woudl increase my performance by greatly reducing back pressure, and thus, reducing load on the engine!

tell me what you think
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member: grampabob

I think that muffler was designed for your engine, and if you mess with it you are likely to regret it.

Bob
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member: xteraco

the eingine on my scooter was designed w/ several things in mind, such as

-reliability
-safety
-fuel economy
-low noise levels <-- this ties in w/ legal issues
-low maintenance
-low production cost

ok, now... we've thought about what the design goals are for the scooter, now, lets think of the fundamental workings of an engine

a 4 cycle engine goes through 4 cycles..no way, anyhoo.. the first is the intake, this is where the piston travels downward toward bdc (bottom dead center) and as this happens the intake valve opens and lets air into the combustion chamber... the second cycle, is the compression cycle, this is where the piston travels toward tdc (top dead center) as it travels upward, the valves are closed, and the air that was taken in is compressed w/ fuel vapor, wich creates a highly explosive mix.... the 3rd cycle is the power cycle, also known as combustion event... this is where an electrical signal is sent to the spark plug, thus igniting the mixture that resides w/in the combustion chamber, and forcefully sending the pistion downward toward bdc again.... this leads us up to our final cycle... the exhaust cycle. The exhaust valve opens up, and the pistion is headed back toward tdc, pushing the spent exhaust gasses outward into the exhaust pipe...

this is where we start to get into the idea of my mod

as the exhaust gasses are passing through the pipe, every turn, uneven surface, chamber or anything that isnt totally smoothe will resist the exhaust gasses from coming out of the combustion chamber, this is known as "backpressure". As the pistion is coming back up during exhaust cycle, the back pressure causes positive pressure, meaning that pressure is pushing out, and also pushing against my piston... this means my piston has to work harder to push the exhaust out, and if it has to work harder to do that, that means it also takes a fraction of a second longer...

if i make the pipe straight, and eliminate the chamber that causes backpressure, in theory, it would reduce backpressure, and make my engine just a little bit quicker, or at least take some load off of it

now, we have to consider, what design goals am i violating here, whats the catch, because no performance mod or anythign comes for free.. so what am i giving up that the manufactures originally designed to be there...

well, if we give it some thought, the chamber is what reduces some of the noise that the exhaust makes, so this would make my engine a bit louder, possibly quite a bit louder.... possibly even so loud that i coudl be givin a ticket.... it might also reduce some fuel economy, but i doubt it...

let me know what you think
~xteraco

First off for proper terms, flaps and objects in a muffler are called baffles. :wink:

Yes, you theories are totaly correct.... Lost backpressure on a 4cycle can allow the piston to return back to return to cycle 1 faster. And, yes, it will be very loud, and depending on the motor's size will it be enough for a ticket.

You do however run a risk of how the engine was ment to work. Some engines use backpressure to aid in the operation of the motor. I do know that all 2cycle motors use sound precussion and backpressure to prevent fuel from ejecting from the cumbustion chamber before the piston can close the exhaust port. This may also be used in 4cycles with overlapped timing....

There are a lot of risks, that's all I have to say... :wink:

Yeah, what rattrap said about using backpressure -

It would be far more beneficial to get a tuned pipe. They are tuned to be just the right length, so when the back pressure builds up, it actually adds power to the engine.

Of course I dont know if you will be able to get a tuned pipe for your scooter.

Look, you won't ruin your engine by removing the muffler, nor will a car's be ruined by removing it's muffler or cat converter. Worst thing, your performance and fuel economy may suffer instead of improve.
But think about this: even weeny 3hp lawnmower engines use mufflers. I've heard one without, and it's frickin' loud. I don't know what power your engine has in it (my guess is between 10 and 20...just a guess, though). In any case, it's going to be more than a 3hp, and so, with them noise-pollution laws, you will get a ticket for not having a muffler.

@Kiz: You could take a normal one and adapt it to fit. That way you could remove a lot a back pressure and keep a semi quite motor. Tho, finding one that would work correctly on a small motor might be a challenge. Some might create greater backpressure than the scooter's small motor can handle.

Also, really only problem would be noise,. Most likly no one has ever overlapped the timing on a scooter, tho, If you want more power and know how to time a motor, that's not a bad way to go (Overlapping).. Fun thing is, when you back off the throttle on a high rev, the pipe will shoot flames..(If the baffles don't restrict it)

If you did both (Overlap and put in a striaght pipe (A pipe with no baffles like you intend to do)), it should really shoot flames and have way more power. But, it be street illegal from all the noise it make... =\ ... and overlapping burns way more fuel....

:wink:

Edit: @ Zack: I didn't say it ruin it,. just that it might (tho might not), mess with the overall prformance on some motors.... :wink:

Quote:@Kiz: You could take a normal one and adapt it to fit.

Unfortunately, you cant actually do that. Tuned pipes have to be made custom for a particluar engine size and output. Xteraco's scooter will require a tuned pipe made just for that engine.

And yeah - about the noise, without the muffler it would likely be far too noisy to bear, because the smaller the engine, the louder the noise ;)

Quote:And yeah - about the noise, without the muffler it would likely be far too noisy to bear, because the smaller the engine, the louder the noise

That's when you stuff a bunch of socks in it and hope nothing goes wrong (I hope it doesn't catch fire with all of the cloth and heat. . .) :-P

Quote:That's when you stuff a bunch of socks in it and hope nothing goes wrong (I hope it doesn't catch fire with all of the cloth and heat. . .) :-P

Thus vastly increasing backpressure (again) and rendering the entire episode pointless. Hehe.

Quote:Unfortunately, you cant actually do that. Tuned pipes have to be made custom for a particluar engine size and output. Xteraco's scooter will require a tuned pipe made just for that engine.

Quote:Tho, finding one that would work correctly on a small motor might be a challenge. Some might create greater backpressure than the scooter's small motor can handle.

:wink: btw... Did a motorcycle muffler ever cross your mind? That or, if you have enough tools (cutting, metal forming, welding, ect) you could make your own tuned and sized correctly...

I'd still go with overlapping,. but you'd need to know how to time a motor.. Only risk is setting the timing wrong and ruining the motor, but done right it works like this:

In a normaly timed motor, it will stop pulling the total volume at the higher RPMs. When you overlap, you set it so the Intake opens just as the last of the exhaust is being pulled out. This in turn boost how much fuel is pulled into the combustion chamber since the leaving exhaust creates a semi vacuum.

Tho, when you back off on a high RPM rev (w/ load (driving)), the leaving exhaust pulls the fuel striaght thru and it explodes in the muffler (given it's hot enough) making the flame throwing effect I mentioned above,.. Thus waisting a lil fuel.... And also, set the timing wrong and it's a blown motor..

:wink: Read some small motor books, those will come in handy...

i actually found a haynes book for chinese scooters, so i'm in luck w/ the book thing.... as far as motocycle mufflers, i did think of that, i just dont have the $$ right now