Vintage Expansion Chambers

[Jeff Campbell]

here are a few drawings of vintage expansion chamber design ideas. I'm working on an article, showing the history of pipes, the design ideas behind them, and methods for making such pipes.

Jeff

[note: new message board feature allows users to easily upload photos and attach text comments to photos]

[Jeff Campbell]

added some more drawings above for reference. Anyone that can, please contribute more vintage pipe drawings/dimensions. I would like to get drawings for the pipes below, but don't have ones to measure.


GEM early alumumim Pipe (note photos I have, with different center lengths, anyone know about this?)
Margay Ram Horn Pipe
C & H

[Walt Zahn]

Hi Jeff,
Here is a picture of the one that is on our restoration project. It's connected via a GEM u-pipe. I noticed that the skinny exit tube extends about 1/2 way inside the chamber. What is the purpose of that?
Walt

[Rob Voska]

Stingers that extend to the center of the chamber at the largest diameter were trying to keep noise down. The working pressure in the system is lower there.......but it didn't work well.

[steveohara]

Rob, Your statement about pressure within the expansion chamber caught my attention. What is your source for that remark? Have you done some testing with measuring devices that showed those results? Are you quoting something you saw written elswhere? If so, do you remember where you found that info? I would be interested in seeing the data and testing methods employed to generate those results.

I have built may pipes over the years with inverted stingers and I never found them to be different in terms of sound ouput. The inverted stinger designs usually produced the same effect as shortening the rear cone producing a narrower power band and higher peak power. The introduction of a tube in the middle of the converging cone has a significant effect on the formation of the wave front as the cross sectional change becomes non linear when the tube is stuck in the middle of the rear cone.
I have not done any reading on the subject in many years so I would be interested in looking at any recent research containing new info.
Regards,
Steve O'Hara

[Rob Voska]

Gordon Jennings, Roy Bacon, John Robinson and A Graham Bell. They ran long stingers into the belly of the and even ran them out the side of the belly. Remember most all info you find is bike related and the WOT / driveability is much different.

I used to really be into this stuff in the 80's & early 90's but the dumbing down of karting to nothing but a canned Yam.......has killed the sport and a lot of my enthusiam with it.

[steveohara]

Hi Rob,

I was hoping there was some new writing on the subject that utilized modern technology to measure actual pressure and wave front behavior in the pipes. Long ago I read all of the writings many times over from the "experts" of the 60s and early 70s. You could add Blair and Bossaglia amoung others to the list of researchers that sought to offer some better understanding of the dynamics in the two stroke engines and the pipes. Through the later half of the 70s I worked closely with George Bosco, and engineer at Aerojet General in Irwindale and a former karter and engine builder on many pipe designs. In the mid 70s George collaborated with Blair to write computer modeling programs to evaluate theoretical changes to two cycle engine and pipe designs and their work was interesting but not very productive in the way of useful performance gains. (In those days a home computer took up a whole room and you input your code with punched cards!) In the end, none of the written literature of the era was even close to accurate in predicting the shape that best suited the McCulloch engines. The formulas for pipe design back then consistently produced pipes that had too little volume, too long a front cone and too long a header. There is no question in my mind that Gary Hartman understood the black art of expansion chambers better than anyone in karting back in the days of unlimited pipe development. By 1979 my own R&D on the pipes for alky burning Mac engines with stock ports was way out on the flat part of the development curve such that I could predict very accurately the effect of relatively small changes in the dimensions. The interesting thing was I would have never got there based on any of the well known author's formulas or theories. All the credit goes to Gary Hartman for being willing to build pipes that were dramatically different from the conventional wisdom of the day. I just took his designs and fine tuned them to a very fine degree.
If you ever run across any current research articles dealing with pipe design please give me a shout to point me in the right direction to see them.
In the meantime, for any of the vintage karters that are thinking of building your own pipes here is a good rule of thumb....... use the design formulas that are out there and then make one small adjustment..... increase the diameter at the largest point by a third to a half and leave all the lengths tha same. The cone angles will be much steeper and the volume much larger than the formulas will generate without my little "adjustment" and you'll make more power and have greater engine life.
Or, you can just buy a Blimp and be done with it LOL
Regards,
Steve O'Hara

[Rob Voska]

Steve.... as we have both spent a large part of our lives thinking about how to make a 2 cycle engine run faster what did you think of the mid 80's Vevy pipe?

Also I ran Mako pipes from Al Nunly for a lot of years and still have them. I liked his theory's and it was understandable. We ran a SM on a Komet 135 stock reed that would shifted gears 1/3 of the way down the straight when the weather and flex were right.

Later when I got into running long track stuff with piped yam's I did lots of work with headers.
I'm stuborn and still not sold on a lot of the new stuff. Seems like it's better to have a 30' trailer than to be fast!

[Bill Pryor]

I have built may pipes over the years with inverted stingers and I never found them to be different in terms of sound ouput.

I guess I was lucky and have had completely opposite experiences. I build chambers for Kawasaki 500's in 1970 and they were race pipes with inverted stingers and were intended to be run on the street. We had no other silencers on them and although they were not as quiet as a mufflered bike, they were far quieter than the pipes with conventional external stingers. We didn't run them in part way though, they extended all the way in and were flush on the outside.

So recently when Davis was coming up and they required the noise to be cut down as much as possible I had to find a way to quiet down the Ram's Horns on my 820's so I took off the curved external stingers on them and made some stingers that were inverted into the pipes. The result was that the pipes did not have any of the sharp crackle they do with the external stingers and overall they "seemed" much quieter. And no, I do not have any quantitative results, it was just subjective. Maybe the lack of crackling is what made them seem much quieter. I did have the noise "police" at Davis specifically listen to them and they said they were at least as quiet as any of the dual engined karts out there with mufflers.

[steveohara]

Rob,

The "Vevy" pipes I saw were pretty effective as they had perforated rear cones that made them effectively larger in volume than they would have been if the rear cones were solid. Most of the modern day direct drive pipes are basically "Vevy" pipes and they work pretty good and many different types of engines. I never ran the Mako or Mayko on the Macs but I remember the name. Isn't that the brand that made the "parabola" pipe? It seems those pipes had trumpet shaped front cones and parabolic shaped rear cones and George used to say that they fit the computer models very well but nobody ran them in the enduro stuff much so I don't how they worked. I seem to recall running one on a KT100 sprinter back in the late 80s and it was about the same as a Blimp but it's been too long to be sure.
In general, for Mac engines the key is to make them BIG.... it was the small stuff like the Kendick, IKS, D-H Torque pipe, and even the early Gary Hartman and KH pipes that killed the motors. There was a stretch in the early and mid 70s where everyone was building pipes with 3.5" diameter center sections and those pipes just didn't have the volume needed by the Mac engines.
Bill, Thinking back, I'm pretty sure all the inverted stinger pipes I tried came after the can rules came along so the noise issue was covered up by the silencing can. I remember a lot of the 2 cycle street bike pipes had very long inverted stingers made of perforated tubing and they were much less noisy so it makes sense that you got a similar result with yours. It's been so long since I was involved with that stuff..... where did the years all go
Regards,
Steve