Exhaust Exhaust Port- Muffler-Gasket

Discussion in '2-Stroke Engines' started by BoltsMissing, Apr 10, 2008.

  1. BoltsMissing

    BoltsMissing Active Member

    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 ?

    Last edited by a moderator: Apr 10, 2008

  2. azbill

    azbill Active Member

    my guess would be
    'Made in China'
  3. sparky

    sparky Active Member

    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.
  4. BoltsMissing

    BoltsMissing Active Member

    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 ?
    Last edited: Apr 10, 2008
  5. sparky

    sparky Active Member

    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..."
  6. BoltsMissing

    BoltsMissing Active Member

    Correct Sparky ! Is your middle name "Bright" ?
    Or "Brighter" ?
    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 ?
  7. KiDD

    KiDD Member

    Why not fab up some adapter plate if you think it will help airflow?
  8. BSA

    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.)

  9. sparky

    sparky Active Member

    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.
  10. loquin

    loquin Active Member

    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.
  11. BoltsMissing

    BoltsMissing Active Member

    Thanks forumites,

    BSA, that's the type of answer I was looking for, very good lead.

    Researched using Google and I came up with heaps of other answers and more leads using the word Coanda
    However, Sparky's answers DOES have merit, the Chinese are probbaly trying to perfect the Coanda effect to, or they have and won't tell, or they are giving us all a clue to lead us to something else.

    Some of the graphics show a basic explanation of air flow and Coanda Effect principles.
    See Exhibit A.
    Then it gets rather interesting, it goes to magnets !
    The Coanda effect in principle using magnets, an untested theory so far showing magnets moving a rotor !
    See Exhibit B.
    Other exhibits show flying saucer experiments using Coanda Air Flow.

    Another interesting find is here:More to the point, but not the actual answer, I think.
    In particular where it where it say's
    The present invention relates to measures stemming from the above-mentioned study and from the Applicant's earlier patent, so as to delay the flow of mixture in the combustion chamber relative to the flow of the air contained in said chamber, thereby tending to avoid loosing mixture via the exhaust. The cavity constitutes a retention space because it reflects the air flow thereby setting up a flow in the opposite direction to the flow of mixture inside the cavity, thereby momentarily stopping said mixture flow at the top of the chamber.

    Research is now ongoing...,
    1.To modify Standard HT Exhaust Gasket and Muffler pipe to match engine's Exhaust Port ( as exported from China) or not to modify ???
    As Kidd sugested, an Adaptor Plate.
    Has anyone one gone and made a adaptor plate, did it make much difference ?

    2. Why did they change from what's used in China to what's exported to everywhere else ? ( who cares really, we fix them anyway.)

    3. Is this the basis for a ongoing "who dunnit conspiracy theory" on the HT Exhaust Muffler and Gasket Mismatch ?

    To be Continued...! ( if time permits)

    Attached Files:

  12. sparky

    sparky Active Member

    Good luck finding any difference thru the exhaust with modified aftermarket gasket. Even an adapter plate won't create better flow from what you've already got. There's not much else to say on the matter.
    Last edited by a moderator: Apr 10, 2008
  13. KiDD

    KiDD Member

    So the exhaust port on the HT is square? BUt the exhaust header is round? or is it the other way around?
  14. BoltsMissing

    BoltsMissing Active Member

    I am doing another build, my second build infact and taking my time to question things as I go.

    A brand new kit, when opened the exhaust gasket is already held on the engines exhaust port, with the bolts and washers finger tight.
    Thats how it's packed.

    The centre hole of that gasket is round, the outlet of the engine's exhaust port is rectangle.
    Also, the centre hole of the gasket partly covers the port because it's smaller than the rectangle.
    So a build up of muck is obviously going to occur and some restriction.

    Whats strange though, the muffler's flange where the gasket tightens on is a perfect match, round.
    This is not a obvious mistake by the manufacturers, is it ?

    Like I have said on the first post of this thread, I took the engine and the muffler to a engine reconditioner yesterday to ask for an opinion and he said of all his 30 years expirience of re-building eingines, he does not recal odd shaped exhaust ports and muffler flanges on 2 strokes. They all suppose to match.
  15. KiDD

    KiDD Member

    Can you post some pictures?
  16. sparky

    sparky Active Member

    I promise that that excess gasket on the inside will be burnt off from the hot exhaust gases... so there will be no mucky buildup or restriction.
  17. KiDD

    KiDD Member

    I just want to see it... I'm not fully visualizing this.
  18. BoltsMissing

    BoltsMissing Active Member

    I don't have a camera, but planning on getting one soon.
  19. fastboy9

    fastboy9 Member

    Yep exhaust port on engine is a rectangle, that way as the piston moves down the gasses are exiting at an equal rate, but then the exhaust pipes header is a circle to fit the pipe, and the gaskets are obviously designed for the pipe. I dont think this is designed this way, my best bet is it is more economical and cost effective for the original manufacturers in China to buy in the exhaust pipes, perhaps there original use is for something else? I purchased my kit from china off of eBay and am quite friendly with the guy, his english not so good, he sent me a postcard though for chinese new year! I'll ask him why that is, maybe he has a better idea. I know that he does look at this forum though...

  20. BoltsMissing

    BoltsMissing Active Member

    Thanks, if your man in China can clarify this minor glitch it would help solve the riddle.