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Do all motorcycles utilize exhaust scavenging?

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Discussion Starter · #1 · (Edited)
I created a discussion (out of the post that I had linked previously)
bennyrides' Write-Up on Basic Exhaust Operation

It discusses the theory behind exhaust operation.

I am consistently adding more information regarding the components of exhaust design.

My questions for MotorcycleForums.net members
  • Does the Yamaha R3 321cc scavenge?
  • Do all motorcycle engines scavenge?
  • What is your understanding about "back pressure" and how has it changed after reading my write up on R3-Forums.com?
I was going to post this in the Yamaha forums, but I feel that ehxaust operation is a more general and broad topic than relating merely to Yamaha, so I put it here in Mechanic's Corner.

I will be available to debate my claims and I will correct "erros" if I find reason to (for example: you reply debating a section, providing your reasoning & sources of information).
 

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Welcome......I think.
First, I have removed the link in your signature because it makes me nervous since you have no history here.

Then, whether an exhaust system presents back pressure or negative pressure (scavenging) to the exhaust ports depends on the design of the engine and the manifold and the pipes.

Engine design from a racing performance perspective can't always be applied to street machines.

You seem to be saying that "back pressure" is a myth and I quite assure you that it is NOT.
Not sure what this discussion will accomplish but go ahead and we'll see where it leads.
 

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Discussion Starter · #3 · (Edited)
Then, whether an exhaust system presents back pressure or negative pressure (scavenging) to the exhaust ports depends on the design of the engine and the manifold and the pipes.
What is your understanding of the differences between back pressure and negative pressure?

Engine design from a racing performance perspective can't always be applied to street machines.
From what I have learned, you're correct about the performance perspective between racing and street machines; it's a complicated topic where I feel each one gets entangled with the other.

You seem to be saying that "back pressure" is a myth and I quite assure you that it is NOT.
What is your definition of "back pressure" and what are your thoughts surrounding why I am reading that it's a myth?
 

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As far as I am aware scavaging is restricted to two strokes which use some of the outgoing exhaust gasses to help draw in the fuel mix entering via the transfere port. Four strokes do not need this as the exhaust is pushed out by the rising piston on the exhaust stroke where the only opening is the exhaust valve. Two strokes on the other hand rely soley on the bottom of the piston compressing the fuel/air mixture in the crankcase sufficiently to push it up the transfere port.

Back pressure is where there is some restriction against exhaust gas being pushed out allowing it to cool somewhat, and therefore keep, the temprature of the exhaust valve down from combustion temperatures....but I could be mistaken....
 

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What is your understanding of the differences between back pressure and negative pressure

What is your definition of "back pressure" and what are your thoughts surrounding why I am reading that it's a myth?
I'm not sure what your motivation is with coming here with the expressed purpose of starting THIS discussion.......which I have no desire to participate in.

On a gas engine that has bends and twists and a muffler with real baffles and maybe even a CAT converter, which all combine to slow the flow of exhaust gasses as they go farther down the pipe, it is pretty much impossible to NOT have some back pressure at the exhaust port.

Think of a freeway that is FULL of vehicles and the ones at the front are going slower than the ones at the back.
The ones at the back will quickly feel the pressure from the ones at the front.

As far as "what you are reading", the Internet is an excellent vehicle for spreading information at the speed of light.
It also is capable of spreading lies and mis-information quickly too.

Self appointed "experts" are often wrong, sometimes with malicious intent and sometimes just out of stupidity.
 

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Discussion Starter · #6 · (Edited)
I come here because I had the expectation that MotorcycleForums.net was home to a wide variety of specialists regarding air & fuel delivery, engine mechanics, exhaust systems, and thermodynamic characteristics of exhaust flow.

I was hoping that by submitting this thread, I could get some feedback on the thread I wrote on the subject, to sort the logic, reasoning, and understanding therein.

I will wait for other replies if you do not want to participate.
 

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Discussion Starter · #8 · (Edited)
Response to Easy Rider
@Easy Rider, I've done nothing wrong to you; I merely responded and took into consideration the following:

I'm not sure what your motivation is with coming here with the expressed purpose of starting THIS discussion.......which I have no desire to participate in.
Your words are hurtful, unproductive, and condescending.
I'm sorry this topic makes you feel sour.

If you do not want to participate in a discussion the best thing you can do is unfollow the discussion and ignore it's progression.

About the topic
I've updated my post to include an edit of @intimid8er's EXHAUST--Buyers Research Guide to clarify the introduction of its contents.

Also, I created a discussion (out of the post that I had linked previously): bennyrides' Write-Up on Basic Exhaust Operation
 

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Your words are hurtful, unproductive, and condescending.
I'm sorry this topic makes you feel sour.

If you do not want to participate in a discussion the best thing you can do is unfollow the discussion and ignore it's progression.
I am truly sorry if I offended you.

It is just VERY unusual for someone to jump into a forum like this with no introduction AND a first post that looks like it is designed to stir up an argument.

You do understand what a moderator is, right ?
 

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I'm being serious here (no nonsense; just my experience) - when we work with people who are combative and provocative, these experiences will change our perception of everyone else we deal with.



Your job as Moderator means you have to make judgments based on your past experience and limited awareness of current situations. I understand your struggle.

]I personally don't have any interest with Introductions; I find them useless. As I understand forums, they are designed to provide a platform for us to help each other with problems and discuss things we find mutual interests in.

Let me preface "My suggestion" with the fact that yes, I am new to the forums - which means I have no idea who or what was happening on MotorcycleForums.net before I joined three days ago.

I am also not a Moderator of any kind, so I cannot imagine how many people, posts, and problems you're asked to handle on a daily basis (you don't have time to dabble with the possibility that things will be "just fine"). Decisions need to be made.

My suggestion: Allow people to arrive before making judgments. Allow them to start the discussion; if it gets out of hand, then step in.
 

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My suggestion: Allow people to arrive before making judgments. Allow them to start the discussion; if it gets out of hand, then step in.
You have arrived now. And not smoothly.
I have edited your last message extensively because it was a confusing mess in it's original form.

So far, you just don't fit in with the "normal" flow of posts on here.
And I don't see the differences as being interesting or useful.
And I don't see your posting style as being "cute" either.

I may very well decide that I "have no use for" anyone with your attitude about introductions.

I am fighting a desire to just kick you off and be done with it.
But I think you can contribute something useful if you try.
Help me out here.
 

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Discussion Starter · #12 · (Edited)
Everything I do here is apparently wrong.
I can't function with a tyrant hovering over my shoulder.

Don't believe everything that you think.
You're just a bully.

I'm not going to conform to your expectations to fit in.
Just get it over with.
 

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I believe my post was accurate....scaveging and back pressure are two entirely different things specific to engine types. I'm sure ER will get over it as you succincly suggest...I have a feeling your four day membership is all you will have.
 
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