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

Looking for OS 108 header

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Old 05-13-2011, 05:54 AM
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kmtranmd
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Default Looking for OS 108 header

I have an OS 108 FSR and some 90 size pipes laying around, but no exhaust manifold and header for the little beast.
I'd like to buy manifold and header from someone if you have them laying around with no home.
I also need help with approx pipe length for this motor for propjet application if someone knows the info.
Thanks,
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Old 05-14-2011, 02:49 PM
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Pylonracr
 
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Default RE: Looking for OS 108 header

The header is the easy part. Macs sells headers for almost any engine made, and you will probably not pay more than about 30 bucks for it. The nice thing about these is you can pick the offset from centerline to clear your fuselage.

The pipe length is another matter. There are so many variables I have found it almost impossible to recommend a starting point. Prop, fuel, altitude, primary cone diameter in the pipe, and intended RPM range all factor into pipe length. Here is the short story on how to tune the pipe.
First run it with an open header (no pipe or muffler) and a prop 1 sizelarger diameter than you plan to run. Record the RPM. It will be loud and not idle with no pressure. Put the pipe on at full length and record again, shorten pipe 1/2" at a time until it is higher than open RPM. Shorten pipe 1/4" at a time until RPM no longer increases. The pipe is now too short for the prop on it, so go to thesmaller prop you planned on running on it (remember, tune the pipe with alarger prop). You now have the pipe tuned. Change props or nitro content and it is no longer theoptimum length. I usually stop when the RPM increase is only about half of what it increased on the previous 1/4", this leaves the pipe a little long.

Slightly long gives you a broader high speed needle setting at the cost of 100 or so RPM. Short pipes are more peaky, give a hair more power, and are VERY sensitive to needle settings.
Choose your comprimise.
Good luck
Scott.

Feel free to PM me if you have any questions. It is really pretty easy, it just takes a little while.
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