Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Tuned pipe couplers

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Old 09-11-2002, 01:35 AM
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Keefer
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Default Tuned pipe couplers

I'm breaking in a Rossi 45 side exhaust with a tuned pipe, and as a normal practice I run the RPM up to peak for brief periods (15 seconds) then back to rich. While I'm doing this, I'm change the pipe length and measure RPM and pipe length.

Here's my questions:
1 - the 3/4" silicon coupler I'm using won't tighten up very well using just zip-ties (Aerotrend Creme coupler) and I think the next size down won't fit the header. Ideas?

2 - The pipe fits over the header and slides easily. Should I cut the header such that there's no overlap of the header and pipe, or is overlap OK?

3 - the instructions (what few English portions there are) describe a pipe length for 15K RPM at 10.5 cm for a Rear Exhaust engine. How do I measure this for my Side Exhaust?

Thanks, in advance, guys!
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Old 09-11-2002, 02:15 AM
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Default Tuned pipe couplers

1. Double up the z-ties or use a small metal hose clamp. The end of your pipe needs to be supported also, this will help the problem.

2. DO NOT OVERLAP THE PIPE AND HEADER. Metal to metal contact plus vibration equals radio interference. Leave a minimum 1/16" gap.

3. Use a flexible tape or a piece of string, to measure around the center line of the header and add it to the pipe length.

Hope this helps.
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Old 09-11-2002, 11:19 PM
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Default Tuned pipe couplers

Painless - thanks!
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Old 09-12-2002, 01:43 AM
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Default Tuned pipe couplers

Looking at your original post, 10.5 cm is 4.13 inches. That seems way to short for any sort of a tuned pipe measurement. What exactly are they having you measure?

The correct way to measure a tuned pipe is from the face of the piston to the middle of the rear cone. This is the average distance the sound pressure wave travels. The length is RPM dependent.
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Old 09-12-2002, 02:04 AM
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Default rossi pipe

I have a morris 45p side exhaust with long pipe from Morris hobbies. it is19 inches from exhaust to end of pipe. Thats with a 10x5 prop and it turned 17,500. I also have tuned silencer which I dont have exact measurment for but is closer to 7 inches and it turns a 10x5 15,500. The coupler that came with it is so tight i dont have anything holding it together.
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Old 09-12-2002, 02:59 AM
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Default Tuned pipe couplers

Those RPM's sound pretty typical when switching from a silencer to a true tuned pipe when using the same prop.

The only way to set tuned pipe length is through testing. Most headers and tuned pipes come to long for a particular application(on purpose).
Cut 1/16" off the pipe (inlet side) and set the gap between it and the header at 1/16", you should see an increase in RPM with each cut. When you don't, you have gone to far, just set the gap at 1/8" to get back to the previous setting. Each increase in RPM will also require a ckick or two richer needle setting. Don't hesitate to try different props with each setting too.

This final tuned pipe setting is for a particular prop and nitro percentage. If you change anything, like smaller prop and/or more nitro the pipe will need to be shorten because of more RPM. If you use a bigger prop and/or less nitro the pipe will need to be lengthened, less RPM.

Increasing the gap between header and pipe is Ok to a point, but you run the risk of blowing out the coupler.

Its all about timing, the time it takes for the pressure wave to reach the piston face. More distance=more time. Less distance = less time. Thats why the length is RPM dependent, the faster the piston is moving up and down the less time between pressure waves and the shorter the pipe needs to be.

All these principals are explained very well in a book called "Two stroke tuners handbook" By Gordon. Its no longer in print but most well stock librarys will have it.
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Old 09-15-2002, 07:01 PM
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Default Tuned pipe couplers

Originally posted by PAINLESS
Looking at your original post, 10.5 cm is 4.13 inches. That seems way to short for any sort of a tuned pipe measurement. What exactly are they having you measure?

The correct way to measure a tuned pipe is from the face of the piston to the middle of the rear cone. This is the average distance the sound pressure wave travels. The length is RPM dependent.
That's the measurement Rossi calls out from the exhaust port of a rear exhaust engine to a raised circular ring about 50% down the length of the pipe (where it changes from divergent to convergent). The pipe I'm using doesn't "converge" on the back half, but the ring is where the diameter becomes constant. Is this a good place to call the "middle of the rear cone"?
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Old 09-15-2002, 07:43 PM
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Default Tuned pipe couplers

Everyone measures it differenty. I would do it the way they told you, but don't be affraid to experiment. Move the pipe 1/16" in either direction and see if you get an increase in RPM. Although that number still seems short, but I have no experience with Rossi pipes. I would hope they did some testing to arrive at that measurement, but again, different props and nitro content effect pipe length.

The convergent cone or tail cone is what reflects the sound wave back at the exhaust port. Since this cone varies in length from pipe to pipe the best way is to find the middle of its length and use that point to measure to.

Correction: the book I mentioned above was written By "Gordon Jennings".
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Old 09-16-2002, 09:15 PM
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Default Tuned pipe couplers

Keefer,

Go to Macs Products web page and read their tuneing info page. May help. very informative.

http://www.macspro.com/

Tom...
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Old 09-18-2002, 12:26 AM
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Painless and tknobby - thanks!!
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