I am planning on making an expanson chamber type exaust for a small gas engine. Does any body know of a design program that is reasonably priced (or freeware) and would tell me what diameter and length to make the header, size and length to make the cones and stinger?
Any help would be appreciated!

Thanks,
Pete

Good luck-- the programs I have seen are not applicable to anything but all out speed effort - then - they are still just a wild ass--guess
are you after max power -at one rpm--or after more power at full throttle whilst retaining proper throttle response throughout the entire power band .
Pipes can do lots of things -but unless you outline the type response you want from the engine -- you can simply waste your time .

Hi dick,
I am looking for more hp and a broad power band. I am trying to get as much out of this engine as I can it is going on a Funtana 90. I think I have read a couple post were you had
done this same thing with a Roto 25 I think? Weren't you working on some pipes too?
What kind of results did you end up getting?

Thanks,
Pete

Hi Pete,
I found an article that may help you. When you make your expansion chamber, the header pipe lenght should be adjustable. The stinger (tail pipe should also be on the large side so that you can insert a smaller tube to vary size, lenght and position. You have to play with these adjustments until you get what you want. Remember the gain comes from allowing an advanced exhust port and improved scavaging. This is true even with stock exhust timing and correct pipe configuration.

Enjoy, Dave

http://www.motorcycle.com/mo/mcnuts/em-pipes.html

Dave,
That makes sense, I think? Where did you find the article that you are talking about?

Thanks,
Pete

Dave,
The link is there now thanks. I will read through it and see what I can make of it.
Pete

delete

My ROTO on the tuned CF pipe (Ed Skoerpa ESComposites) really works.
I set it up for good response in 8000 9000 range.
This still provides nice throttle up from lower rpms .
You simply MUST put together your setup -on a proper bench and try prop pipe combos and listen to response at various points in the power band -right from idle.
This is not a "bolt on and go" deal.
Or copy some one elses setup then wonder why it doesn't work for you.
It is a concept of power tuning you must learn to work with - correct prop -needle setting heat - etc..

Dick, Thanks for the advice. I like working on my own designs of things when I have time,
and I'm sure this will be a learning curve. I hope I can figure it out. It just seemed to me that we are missing out on a lot of power not using expansion chambers.

Any other advice is appreciated.
Thanks,

Pete

[link=http://www.mh-aerotools.de/airfoils/javapipe_en.htm]Tuned Pipe calculator[/link]

Hi FastRat,
That calculator is awsome. You can slide the value adjustors to see how RPM etc effect design. It all makes sense. Thanks.

Dave

Use it - let use know how it works for you.

Larry,

Thanks for that link I had heard of that site but was unable to find it. Very interesting, have you ever used it to design a pipe, if so how did it work?

Thanks again,
Pete

Hi Dick,
How much thrust are you getting with your Roto and with what prop?

Thanks,
Pete

I haven't gotten alot done on this project but I did manage to widdle out a proto-type exaust manifold today. What do you guys think of it?

Pete

17x6 prop -and thrust was 13 lbs as I recall -on that prop -
I am going to put it in another plane -sold that one a while back -
Thrust means something -only when comparing
I wanted a prop which flew the model smartly as well as delivering decent static thrust --I used an APC

Dick,

Was that enough to 3D fly the Funtana. Also where did you find a 17x6 APC I cant seem to locate one?

Thanks,
Pete

It worked - not really great tho -