Pipe design

flattop1

Dawg 89
The converging cone and stinger .
Short sharp angle on the converging cone vs long gradual taper
Short sharp is that the more peaky high rpm design ?
How about the stinger what effect is a bigger diameter vs smaller same principle small short diameter creates a faster more powerful return wave ?
 
the steep taper is more power in a smaller rpm range and the smaller stinger hole changes the pressure/speed of sound in the pipe.
 
two stroke performance tuning book. I have made pipes from scratch with this books info. I cant tell you off the top of my head any helpful info--its been a while
 
There is a good chance the current pipe designs are optimum .
Would like a way to judge a pipe by size and shape .
One problem is the stinger and converging cone are under the muff .
The book is in depth and takes a while to take it all in .
 
We spent considerable time tuning 2 strokes in the 1980's, with limited success.
Gordon Jennings, "Two Stroke Tuners Handbook is one of the few things I'd attempt to save from a total house fire. It is the holy grail of experimental tuning of more than just 2 cycle engines.

The steeper the angle of the converging cone the greater the reflection wave and it will chop the RPM at a pre determined point. OEM motorcycle pipes use this as a rev limiter.
A more gradual angle of the converging cone the more the engine will "string out" or continue to climb RPM with a sacrifice in peak power.

We experimented with the outlet pipe diameters extensively. You will feel .025" ID change in the seat of your pants.
The outlet pipe ID controls the pressure of the return wave pushing the over scavenged fresh mixture back into the exhaust port.
If you consider the after market expansion chambers of today are well designed quality units. I submit they are probably very close to optimum.
BUT, to send pipes all over the country to different weather conditions, altitudes, engines, length of races and amateur tuners. There must be a certain amount of safety built in or your product would get the reputation as an engine killer. So IMHO they make the outlet pipe ID a little too large. In the case of the brand and style of pipes we worked with in the 1980's,,,,,,, some were .050" too large.
Decrease the ID .075" was fast full range but the piston crown would suffer. You could watch the CHT rapidly rise no mater of the fuel mix.
At .100" smaller the clutch engagement changed, she felt strong pulling out of the pits but went flat and hot long before max RPM.
Larger outlet pipe ID from manufactured and the pipe was slow and cold.

We welded a large thick washer to the end of the outlet. Reamed it .100" larger. (we didn't know at the time were it needed to be) We drilled and tapped 3 mounting holes in this washer and had a series of washers with various hole ID's as much as .150" smaller we could fasten to it. In the end .050" smaller than manufactured was best power, range and length of race. Still hot but manageable,, air cooled.

Mr. Nunley manufactured the Maco pipes of the day,, if I'm not mistaken. it will be interesting when he decides to post to this thread.

Best, WP
 
Mr. Nunley manufactured the Maco pipes of the day,, if I'm not mistaken. it will be interesting when he decides to post to this thread.

Thank you Paul. More later.
 
It's called "two cycle exhaust theory". A source of information on that subject comes from Dr. Blair At Belfast University. An engineer friend of mine first introduced him to me in the mid-70s. Using his formulas, I designed several pipes. One for the open foreign engines, one for the Mc 91 and one for the Mc 49er. They were all big hits at the 1975 Quincy IKF Nationals. Over the years the designs were improved on.
I came to understand the fact that; from the carburetor intake to the exit of the expansion chamber is a tuned length. Intake, cylinder and exhaust pipe all work together. I call it the "two cycle event".
I doubt anyone understands it 100%.
My newest creation, unfulfilled wishing in the wind.
 

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About Dr. Blair's formula. His formula starts with the exhaust port opening ATDC, in degrees, and the RPM where the engine reaches peak torque. From this information he determines the segment lengths and the header length. Surprisingly, the header length and the stinger length were both substantially shorter than the pipes of the day. Dr. Blair's formula also included the two angle diverging cone. Today, most pipe builders neglect that very important feature. I took it one step further, I made the diverging cone with parabolic curves. I also use parabolic curves on the conversion come. Look up parabola.
 
Thank you, I own the book. Lots of really good information. I've been reading Gordon Jennings since the early 70s. Got a few of my best ideas from him. I built a McCullough reed open in the mid-70s using some of his ideas. I won the Northern California open McCullough class with it. I won every race I ran except for one. I blew up the Hartman clutch on my first race. I did have fast time. Dave Knapp had second fast time
 
I actually assumed you did. It was actually intended for others. Hoping your health hangs in there. I still have one of your original Mayko SL's from back in the day. For being a super low bottom end pipe it has impressive over run on a Kt100. Oh, and last summer I was on the track at the same time as Tab. Wished you could have been there. It was a bucket list experience that I didn't even have in my bucket until it was happening.
 
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Excellent link , a must read/have .
Using theose techniques you could build a very nice engine ,2 or 4 stroke .
 
Pipe volume .
I have noticed that almost all of the Reed valve pipes I have are small volume
Compared too the kt pipes .
This seems odd , or at the least opposite of what I would expect .
 
It's called "two cycle exhaust theory". A source of information on that subject comes from Dr. Blair At Belfast University. An engineer friend of mine first introduced him to me in the mid-70s. Using his formulas, I designed several pipes. One for the open foreign engines, one for the Mc 91 and one for the Mc 49er. They were all big hits at the 1975 Quincy IKF Nationals. Over the years the designs were improved on.
I came to understand the fact that; from the carburetor intake to the exit of the expansion chamber is a tuned length. Intake, cylinder and exhaust pipe all work together. I call it the "two cycle event".
I doubt anyone understands it 100%.
My newest creation, unfulfilled wishing in the wind.
Looks a lot like BRC. Pipe
 
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