Yamaha Headers

Ted Tucholski

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I have heard more than once that the Yamaha was designed to be a 125 cc motor. And that since it is a 100cc motor the exhaust hole or port may be to big??? So what would be the ideal size of the exhaust if we could narrow it down. Also is that the reason some header are narrowed soon after the exhaust flange???
 
I have heard more than once that the Yamaha was designed to be a 125 cc motor. And that since it is a 100cc motor the exhaust hole or port may be to big??? So what would be the ideal size of the exhaust if we could narrow it down. Also is that the reason some header are narrowed soon after the exhaust flange???
I just don't know where these rumors get started. lol If it was too big, why do you suppose making it bigger, and/or higher, makes more horsepower?
I can't say for certain why the tapered header works better, it just does. It's what I used.
 
Sure would by nice if 2-stroke headers were marked., I never even thought about it , until I wound up with about 7 different KT headers, guess I'll need to mark any new ones I buy.
 
I just don't know where these rumors get started. lol If it was too big, why do you suppose making it bigger, and/or higher, makes more horsepower?
I can't say for certain why the tapered header works better, it just does. It's what I used.
I'd hypothesize that on a stock Yami the Buller KBDM pipe/header combo made by RLV or any min-reduction header as it tapers increases exhaust velocity speed therefore I'd deduce it would scavenge the engine more efficiently which I'd venture to assume the sooner & more efficiently you get the waste out the sooner & more efficiently U can get a fresh charge into the engine not withstanding back pressure & expansion pipe/chamber functions in addition too the latter. But that's JMHO but then everyone has one right ? : )
 
Honest to god Al I sometimes wonder if you are really paying attention. I never said make the exhaust hole bigger, but I did reference that making it smaller might be better. And if smaller is better .....how small and how far or close to the exhaust should it be.??? Here we go again.
 
How was the KT100 designed to be a 125? When you bore it 55mm the cylinder is super thin at the bottom and when you stroke it the port timing is way off even with the piston popping out the top and even then you can only get 110cc out of it. When you eyebrow the exhaust port it goes faster and there are factory recommended mods to open up the transfers too.

Sundog
 
Honest to god Al I sometimes wonder if you are really paying attention. I never said make the exhaust hole bigger, but I did reference that making it smaller might be better. And if smaller is better .....how small and how far or close to the exhaust should it be.??? Here we go again.
honest to God Ted!!! LOL I never said you said make the exhaust hole bigger! I wonder if you really pay attention when you read my posts?
And you did say "exhaust hole or port". I take that to mean the exhaust port on the engine.
 
Jack, the exhaust can be narrowed in the header. I am after info from someone who can suggest a diameter for that header. Maybe Pete Mueller can offer something here.
 
Yes , please. Also how far away from the flange is the narrowest point. You can PM the info and I will explain to you what I am trying to do with the info.
 
Just how would you make the exh. hole smaller?

I always thought the lip from the junction of the cylinder to the exhaust port could be smoothed with filler to reduce turbulence.

DK
 
Any thoughts on this ?

I'd hypothesize that on a stock Yami the Buller KBDM pipe/header combo made by RLV or any min-reduction header as it tapers increases exhaust velocity speed therefore I'd deduce it would scavenge the engine more efficiently which I'd venture to assume the sooner & more efficiently you get the waste out the sooner & more efficiently U can get a fresh charge into the engine not withstanding back pressure & expansion pipe/chamber functions in addition too the latter. But that's JMHO but then everyone has one right ? : )
 
I can't stop Jack from posting that info if he wishes to. Commenting on Yeti Racing, I'm not sure if scavenging is a product of the header. I would guess the pipe design would be more important. Nunley knows pipe design so maybe he would address scavenging. I can see the header shape having a bigger impact on the pipes return charge. Again I am guessing.
 
I can't stop Jack from posting that info if he wishes to. Commenting on Yeti Racing, I'm not sure if scavenging is a product of the header. I would guess the pipe design would be more important. Nunley knows pipe design so maybe he would address scavenging. I can see the header shape having a bigger impact on the pipes return charge. Again I am guessing.

I believe I stated "notwithstanding ......"
But I was just guessing by increasing exit volume velocity if that wouldn't vacate the engine more efficiently i.e. the quicker out the sooner it can be charged again. JMHO KBuller must've had a good reason for the KBDM required tapered down header design combo matched set with that pipe & it certainly wasn't to make less power ? Because I don't believe the KBDO requires that tapered down header design. Maybe I'm not being clear or I'm off ? Do any of you follow my trend of thought?
 
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The choke in the header lets the pipe work over a broader rpm range and it's a compromise between low end pulling power with a smaller choke and top end power with a bigger choke. It's like a power valve only it can't change size so, for a flat foot track use a bigger hole, for a hair pin track use a smaller hole.

Sundog
 
Sundog - I concur with you on "what" it does/achieves but my theory was more "how" it does what it does per 2 stroke physics.

The choke in the header lets the pipe work over a broader rpm range and it's a compromise between low end pulling power with a smaller choke and top end power with a bigger choke. It's like a power valve only it can't change size so, for a flat foot track use a bigger hole, for a hair pin track use a smaller hole.

Sundog
 
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