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Old Dec 23, 2011, 05:45 PM
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challenger_i's Avatar
United States, TX, Sweetwater
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Designing a Tuned Pipe for a Big Gasser

Ok, I need more help (just ask my doctor!)...

I have never used a tuned pipe with my glow engines, and I am still in the process of setting up a big gasser, so my experience there is limited.
I do know, from dealing with Ultralight airplane engines, that there is way more power available from a gas two-stroke, if it has a correctly-designed exhaust.
The chainsaw-cum-aero engines available today come with either no muffler, or a muffler from the lawn & garden supply. A fair amount of after-market mufflers are basically collector-director devices, and, while quieting the racket, do little for performance.

What I would like is solid information on how to design, and set up, a tuned-pipe exhaust for a 42-50cc engine.

Gentlemen, the floor is open.
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Old Dec 23, 2011, 05:50 PM
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Birmingham, Alabama
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http://www.mh-aerotools.de/airfoils/javapipe_de.htm


or, you can grab a macs header, tune it by cutting down the pipe until max RPM no longer increases & then hooking a long neck aluminum beer can to it.
the worst thing you can do from a power standpoint, is throw a pitts on it.
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Old Dec 23, 2011, 06:19 PM
OCD: Old, Cranky and Disgusted
challenger_i's Avatar
United States, TX, Sweetwater
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Thanks! Very informative!

Ok, humour a dummy: What is a Macs header, and where would One locate such a critter?

Disregard! I found it!
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Old Dec 23, 2011, 06:22 PM
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macs is just a company that makes exhausts for models.


they're most noted for welding flanges to bent aluminum pipes that fit different R/C engines & pre-made tuned pipes.

http://www.macspro.com/default.asp
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Old Dec 24, 2011, 09:37 AM
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Kingston, Canada
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Have played with tuned pipes a bit. The website that Toysrme pointed out is very good. Dimensions are very critical. And they are efficient over a narrow RPM range, in other words, flat out racing.I had one made for a Quadra 42 made by Quadra but it was made of steel and the weight countered the extra performance.A buddy and I built an unlimited Sea Fury for the Reno races that were to be held up here in Quebec but a month before the scheduled race, it was cancelled This weighed 65 lbs and was 108 in. wingspan. Has a Quadra 200 CC racing motor with a tuned pipe that is about 40 in. long. We put it through the middle of the fuse. enclosed in a piece of stove pipe and the exhaust came out behind the trailing edge of the wing. 24 HP. Swings a 22-22 prop for racing but a milder mannered prop for tooling around. This was in the mid 90s and we had a lot of mechanical and electronic problems with 2 rcvrs and on the old 72 system. We did fly it a bit but gave it to my buddys son. He got it going at our last giant scale funfly and worked great with the 2.4 system. Wing is covered with 3 layers of carbon fibre for strength. The wheels are off the ground in the one pic. Not much help but a lttle food for thought.
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Old Dec 24, 2011, 11:32 AM
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challenger_i's Avatar
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Lots of food for thought!

I think I'll build a largish dust bin collector, and call it good!
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Old Dec 26, 2011, 07:46 AM
Will fly for food
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Look to Amazon for 2 stroke motorcycle tuning and exhaust books.

You can make a tuned pipe that is very peaky (small power band) or one with a wider power band. The narrower the power band, the higher the maximum output.
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Old Jan 04, 2012, 08:06 PM
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Making pipes for two strokes can be a real art, factors like the length and diameter of the front and rear tapers and the length and volume of the expansion chamber can make the difference between a torquer with a wide power band and a peaky rev monster that would only be useful on a pylon racer.
If you are determined to design and make your own pipe (which if done correctly can release a lot of potential power) a good book to read is "two stroke tuning" i can't recall the author but a web search should find it.
It contains a wealth of knowledge on porting and pipe design, i have never owned a gasser (plane) but looking at the standard pipes on most of the engines available leads me to believe that they must be very hindered by the very basic "box" that masquerades as an exhaust.
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Old Jan 07, 2012, 08:18 AM
Will fly for food
Maryland
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Are you thinking of this book?

http://www.amazon.com/Two-stroke-Tun...945855&sr=8-13
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Old Jan 07, 2012, 03:14 PM
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Quote:
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That wasn't the one i have read but i am sure it would contain much of the same information
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Old Jan 13, 2012, 12:42 PM
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United States, ME, Stonington
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Originally Posted by Pinecone View Post
Yes, that's the one. I've studied this book to some extent and done some calculations and porting on a Ryobi 31. (See the thread http://www.rcuniverse.com/forum/m_84..._1/key_/tm.htm) It's a great reference. I've not made a pipe yet but am now in the process of locating one for the Ryobi. I've been in contact with Macs and while their pipe doesn't match the java pipe calculator for my engine very well I might give it a try. I would think an outfit like Macs, who've been making tuned pipes for ever, might have worked something out that would work for gassers but I'd like to get some feedback from someone who's tried them before I plunge for the $200 it's going to cost for theirs!

BTW the Jennings book is available for free download on-line. http://edj.net/2stroke/jennings/

diceco
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Old Jan 20, 2012, 07:54 PM
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challenger_i's Avatar
United States, TX, Sweetwater
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Rupert:

I agree. This is why I was looking at a tuned pipe for my gasser.
My experience has been with BIG two-strokes (Xenoah G-34's and Rotax's between 277 and 503 cc) and there is a huge difference in performance between box exhausts and a decent tuned pipe. As an example, the 503 Rotax will only turn a 54x32 prop (2.2:1 reduction drive, dual carb, dual exhaust) at 6500 rpm (engine rpm) with a box exhaust, vs the same engine, and a tuned exhaust, turns a 54 x 37 at 6800 rpm (engine rpm).
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Old Jan 20, 2012, 09:56 PM
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Originally Posted by challenger_i View Post
Rupert:

I agree. This is why I was looking at a tuned pipe for my gasser.
My experience has been with BIG two-strokes (Xenoah G-34's and Rotax's between 277 and 503 cc) and there is a huge difference in performance between box exhausts and a decent tuned pipe. As an example, the 503 Rotax will only turn a 54x32 prop (2.2:1 reduction drive, dual carb, dual exhaust) at 6500 rpm (engine rpm) with a box exhaust, vs the same engine, and a tuned exhaust, turns a 54 x 37 at 6800 rpm (engine rpm).
I presume we are talking microlites The two strokes i have had experience with have been in bikes
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Old Jan 20, 2012, 11:24 PM
OCD: Old, Cranky and Disgusted
challenger_i's Avatar
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Yep, them be the critters. I have WAY too many bad habits! My Dad said I should have taken up women and booze, as they would have been cheaper!
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Old Feb 23, 2012, 12:38 AM
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What about a mousse can pipe, has anyone tried that? I'm hopping up a ryobi 31cc and read the entire rcuniverse thread mentioned above. It had a wealth of information, but no one tried mousse can pipe and the only one with a tuned pipe had it in a boat.
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