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Exhaust Exhaust Port- Muffler-Gasket

BoltsMissing

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Jan 31, 2008
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897
On both the 50cc and 70cc, why is it that the standard muffler and exhaust gasket match each others port holes, being round, but it does not match the engines exhaust port being rectangle ?
I did take the brand new engine in it's box with the muffler to a established engine reconditioner to ask for their opinion, and they said in all the years
(30 +) of many engine rebuilds, exhaust ports and mufflers on 2 strokes match.
Is there a reason they don't match on these HT 2 strokes ?

MBC EDIT: THIS THREAD HAS BEEN MOVED
 
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sparky

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Mar 19, 2008
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Definitely because of the "Made in China" part. It should do its job still, but because of the crappy material they use... or feminine bolt tightening skills, it doesn't work without permatex gasket maker.
 

BoltsMissing

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Jan 31, 2008
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897
To say it's "Made in China" is not the real answer this time.
Chinese are not stupid people is what I am getting at.
It's a technical question.
The gasket matches the muffler, but both the muffler and the gasket don't match the exhaust port. Why ?
Would there be a technical reason ? ( rather than take on face value)


But if it still stands that it's because it's "Made in China", do you leave it as it is, or get the gasket and the muffler matching the exhaust port ?
 
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sparky

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The gasket's purpose is to prevent leaks, not to look pretty. You will never be able to get the gasket to match both the muffler or exhaust port since they're shaped differently.

As long as the outter edge is sealed, you'll be fine... but you'd be better off with some type of permatex gasket maker than use the stock Chinese gaskets.

The reason that the muffler & engine's exhaust ports don't match is because they were "Made in..."
 

BoltsMissing

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Jan 31, 2008
Messages
897
The gasket's purpose is to prevent leaks, not to look pretty. You will never be able to get the gasket to match both the muffler or exhaust port since they're shaped differently
Correct Sparky ! Is your middle name "Bright" ?
As long as the outter edge is sealed, you'll be fine... but you'd be better off with some type of permatex gasket maker than use the stock Chinese gaskets.
Or "Brighter" ?
The reason that the muffler & engine's exhaust ports don't match is because they were "Made in..."
Must be "Brightest" ?
==================================================
Has anyone then corrected the exhaust flange on the standard muffler to match the exhaust port
by actually making a new flange and a new gasket so all 3 components ared matched ?

For the Sparkys of this world,
I don't mean matched as in "light a flame with a box of mathces", I mean so they are the same shape, matched ?
 

KiDD

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Feb 19, 2008
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Why not fab up some adapter plate if you think it will help airflow?
 
B

BSA

Guest
Originally these engines were used with a completely different exhaust, and the ones made for use in china also have this different exhaust. Only export models have the exhausts that we know. I suspect that they have different shaped manifolds. The shape of the port is just as important as the size, due to the properties of gases. For example gases cling to surfaces (which I believe is known as the coanda effect.)

BSA
 

sparky

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Mar 19, 2008
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That's what I was referring to by the word matched. I said it 5 different ways that the shape of the gasket isn't going to matter in one tiny bit as long as the outter edge is working properly, sealing the exhaust.

Chances are if you went out of your way to make an exhaust gasket that went farther inside the exhaust... it'd just burn away from being so friggin' hot. Which is why the permatex gasket sealer is more important than fabricating your own gasket.
 

loquin

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Jan 11, 2008
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Well, if there's a discontinuity in the exhaust flow (rectangular port mating to a round pipe would be one) some of the energy of the exhaust is going to be reflected back into the cylinder.

What effect that will have I don't know.

If you take a trumpet mouthpiece and blow through it as if you're playing, there's hardly any volume at all. That's because most of the sound energy is being reflected back. If you. Even if you take that mouthpiece and mount it to a piece of pipe, there's still not much sound being produced - the area of the pips is so much less than the open air, that most of the sound gets bounced back. In audio terminology the impedence of the pips is much less than the impedance of the open air.

IF you flare the end of the pipe like the bell of a trumpet, though, you can get VERY loud sounds being produced, as the impedance of the end of the bell is much closer to the impedance of the open air, and much less energy is reflected back.

The effect you would see with the engine exhaust is similar.
 
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