Where is a good source for instructions on adjusting the length of a tuned pipe exhaust system? I've found instructions on Jett Engineering's FAQs. Just curious if you guys know a different or better source of instructions for someone who has never attempted to get the best performance from a tuned pipe system. I just installed a new Rossi 61 rear exhaust on a T2A MKII that replaced a Webra 61 that was on the plane. I left the original tuned pipe from the Webra in place. Right now I have a 11X7.5 prop on the Rossi and get 13,600 RPM. The Rossi engine is new(break-in accomplished) and had three flights on it today.

Ron,

Glad to hear the T2A MK II w/the new Rossi power is flying well. As far as pipe adjusting, let me get out my Rossi and see what the pipe length is. You measure from the glow plug to the high point on the pipe...let me check my "archives" and I'll give you a buzz tomorrow.

Dan

Ron,

Bolly Props in Australia has quite good book about needed topic, just click on exhaust systems

Book is also downloadable in pdf format in here

BR -Jari-

Ron, I've always had excellent results adjusting pipe length by simply interpreting the sensitivity of the needle valve. Start the process by setting the pipe length to something that you know is likely a bit long which should leave you with a needle valve that's rather "sloppy"....i.e. a quarter turn (or more) required between an obviously rich setting and too lean. From there, shorten the pipe in small increments until the needle becomes rather sensitive. When you reach the point where 1 or 2 clicks of the needle valve provides a sharp transition from rich to too lean, then back the pipe off about a 1/4" and you'll be real close. That should coincide with the engine not sagging in the vertical under load. This method has served me well for my Webra Race 61s and YS 60s, both short and long stroke. I've used both Webra and Hatori pipes although I much prefer Hatori. In addition, each 5% nitro increase allowed me to shorten the pipe by 1/8" with a corresponding slight increase in RPM. i.e. going from 15% to 25% fuel, shorten the pipe 1/4".

Hope this helps.

To start with, 13,600 is pretty good ! Id not complain too much about that if everything runs smooth.

A quick and easy way to evaluate pipe lenghth for an existing install.... leave the pipe alone.

install a smaller prop (try an 11x6). See if the rpm jumps a noticable amount. If it does, pipe may be set a bit short, or about right. Leave it there. If it does not gain in rpm, the pipe is working like a governor, and might be a little long.

Install a slightly larger prop (try an 11x9 or 12x6). See how the engine likes it. If it runs well, does not drop a lot of rpm, and transition is unaffected (in otherwords, it runs fine with more prop) the pipe may be a little bit long for the 11x7.5 and you can probably take another 1/4" off of the header or continue to use just a bit more prop. If it acts up, starts to get hot, refuses to transition or surges ----- its too much prop...... shut the engine down and cool it off. In this case, your pipe setting is ideal for your 11x7.5

Bob

Thanks, bob27s, I'm going back to the RC Field tomorrow and will take the time to try a couple other props and see what the results are. Thanks, RH

There are formulas you can use to finetune the pipe tot the rpm you want, ofcourse your engine must have enough power to get to the very high settings.
Even the diameter of the pipe, and the exit are important, as well as these lengths, and even the endcone, which will define between which rpm's the pipe will work well.
I do have all formulas, but these are already packed as I'm going to move; and they are even the same for 2stroke racebikes, thus diameters are a function of the cc's of the engine as well, if I recall well.
Normallt, the engine is then tuned to maximuml rpm's in regard to it's couple/speed, then the load is idealised due to the gear, in airplanes/rc this is the propeller. Guess it's time we get decent variable propellors available.
I think there are programs available that will calculate the engine load by a certain speed / diametre ?

Hey airbus --

Back in the day, as they say, the Rossi rear exhaust would turn close to 14.5 - 15 on a RevUp 11X7 prop using Cool Power 5% -- remember the Rossi's are/were European engines set up for no nitro. I was a copy cat in those days (maybe still am) and never tried a different prop on an MK Arrow and a few other planes after that prior to going to the YS inthe Aurora type setup. I wish I had numbers for my setup length but I don't. I recall going too short with the header and putting back inside the coupler the piece I had cut off. The needle gets touchy and the engine may burp/surge in and out of being on the pipe when flying. A little long means giving up a slight amount of RPM but with the side benefit of never having to worry about an engine run. I had the luxury (and expense) of the inflight mixture but I hardly ever used it. At the conservative setting/length it was very consistant and easy to deal with. The go fast days were fun -- unfortunately all my stuff is in other hands now or maybe in landfill...

Have fun and good luck!
Tom

Here is a great source of information about tuning pipes on MACS web page.


http://www.macspro.com/tuning.asp

Thanks for all the tuning info. Today I ran the tests bob27s detailed above. I had to do a re-run of the test as my glow plug burned out prior to the last(#4) prop. I did the re-run so all data would be using the same type glow plug. During the second four prop test rerun, the fuel ran out as I was just getting to max rpm on the last prop. While refueling, I noticed a fuel leak which required in home care. So the test will continue when I go to the RC field next. However, the initial tests seem to show the 11 X 7.5 to be a reasonable choice.

Below is the data for several props as bob27s suggested. A short background. I placed a Rossi 61 rear exhaust where a Webra 61 rear exhaust had been. Leaving the tuned pipe, fuel tank and filter, etc. in place from the Webra installation. I used a new Master Airscrew 11 X 7.5(black composite type). The prop engine combo ran well, but I wondered if I was close to what the performance should be. Hence the question at the beginning of this thread. Bob27s suggested trying several different props to see what rpm changes there might be. So below are the results of the test. These were run using an OS #8 glow plug. Also, notice two of the props are the black Master Airscrew composite props and two are APC grey props. These where the ones I had on hand.

Master Airscrew 11 X 7.5 13,950rpm
APC 11 X 6 14,400-14,450rpm
Master Airscrew 11 X 9 13,800-13,900rpm
APC 12 X 9 11,700